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objfloat.c

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  • objstr.c 64.03 KiB
    /*
     * This file is part of the Micro Python project, http://micropython.org/
     *
     * The MIT License (MIT)
     *
     * Copyright (c) 2013, 2014 Damien P. George
     * Copyright (c) 2014 Paul Sokolovsky
     *
     * Permission is hereby granted, free of charge, to any person obtaining a copy
     * of this software and associated documentation files (the "Software"), to deal
     * in the Software without restriction, including without limitation the rights
     * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     * copies of the Software, and to permit persons to whom the Software is
     * furnished to do so, subject to the following conditions:
     *
     * The above copyright notice and this permission notice shall be included in
     * all copies or substantial portions of the Software.
     *
     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
     * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
     * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
     * THE SOFTWARE.
     */
    
    #include <stdbool.h>
    #include <string.h>
    #include <assert.h>
    
    #include "mpconfig.h"
    #include "nlr.h"
    #include "misc.h"
    #include "qstr.h"
    #include "obj.h"
    #include "runtime0.h"
    #include "runtime.h"
    #include "pfenv.h"
    #include "objstr.h"
    #include "objlist.h"
    
    STATIC mp_obj_t str_modulo_format(mp_obj_t pattern, uint n_args, const mp_obj_t *args);
    const mp_obj_t mp_const_empty_bytes;
    
    // use this macro to extract the string hash
    #define GET_STR_HASH(str_obj_in, str_hash) uint str_hash; if (MP_OBJ_IS_QSTR(str_obj_in)) { str_hash = qstr_hash(MP_OBJ_QSTR_VALUE(str_obj_in)); } else { str_hash = ((mp_obj_str_t*)str_obj_in)->hash; }
    
    // use this macro to extract the string length
    #define GET_STR_LEN(str_obj_in, str_len) uint str_len; if (MP_OBJ_IS_QSTR(str_obj_in)) { str_len = qstr_len(MP_OBJ_QSTR_VALUE(str_obj_in)); } else { str_len = ((mp_obj_str_t*)str_obj_in)->len; }
    
    // use this macro to extract the string data and length
    #define GET_STR_DATA_LEN(str_obj_in, str_data, str_len) const byte *str_data; uint str_len; if (MP_OBJ_IS_QSTR(str_obj_in)) { str_data = qstr_data(MP_OBJ_QSTR_VALUE(str_obj_in), &str_len); } else { str_len = ((mp_obj_str_t*)str_obj_in)->len; str_data = ((mp_obj_str_t*)str_obj_in)->data; }
    
    STATIC mp_obj_t mp_obj_new_str_iterator(mp_obj_t str);
    STATIC mp_obj_t mp_obj_new_bytes_iterator(mp_obj_t str);
    STATIC NORETURN void bad_implicit_conversion(mp_obj_t self_in);
    STATIC NORETURN void arg_type_mixup();
    
    STATIC bool is_str_or_bytes(mp_obj_t o) {
        return MP_OBJ_IS_STR(o) || MP_OBJ_IS_TYPE(o, &mp_type_bytes);
    }
    
    /******************************************************************************/
    /* str                                                                        */
    
    void mp_str_print_quoted(void (*print)(void *env, const char *fmt, ...), void *env, const byte *str_data, uint str_len) {
        // this escapes characters, but it will be very slow to print (calling print many times)
        bool has_single_quote = false;
        bool has_double_quote = false;
        for (const byte *s = str_data, *top = str_data + str_len; (!has_single_quote || !has_double_quote) && s < top; s++) {
            if (*s == '\'') {
                has_single_quote = true;
            } else if (*s == '"') {
                has_double_quote = true;
            }
        }
        int quote_char = '\'';
        if (has_single_quote && !has_double_quote) {
            quote_char = '"';
        }
        print(env, "%c", quote_char);
        for (const byte *s = str_data, *top = str_data + str_len; s < top; s++) {
            if (*s == quote_char) {
                print(env, "\\%c", quote_char);
            } else if (*s == '\\') {
                print(env, "\\\\");
            } else if (32 <= *s && *s <= 126) {
                print(env, "%c", *s);
            } else if (*s == '\n') {
                print(env, "\\n");
            } else if (*s == '\r') {
                print(env, "\\r");
            } else if (*s == '\t') {
                print(env, "\\t");
            } else {
                print(env, "\\x%02x", *s);
            }
        }
        print(env, "%c", quote_char);
    }
    
    STATIC void str_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t self_in, mp_print_kind_t kind) {
        GET_STR_DATA_LEN(self_in, str_data, str_len);
        bool is_bytes = MP_OBJ_IS_TYPE(self_in, &mp_type_bytes);
        if (kind == PRINT_STR && !is_bytes) {
            print(env, "%.*s", str_len, str_data);
        } else {
            if (is_bytes) {
                print(env, "b");
            }
            mp_str_print_quoted(print, env, str_data, str_len);
        }
    }
    
    STATIC mp_obj_t str_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const mp_obj_t *args) {
    #if MICROPY_CPYTHON_COMPAT
        if (n_kw != 0) {
            mp_arg_error_unimpl_kw();
        }
    #endif
    
        switch (n_args) {
            case 0:
                return MP_OBJ_NEW_QSTR(MP_QSTR_);
    
            case 1:
            {
                vstr_t *vstr = vstr_new();
                mp_obj_print_helper((void (*)(void*, const char*, ...))vstr_printf, vstr, args[0], PRINT_STR);
                mp_obj_t s = mp_obj_new_str(vstr->buf, vstr->len, false);
                vstr_free(vstr);
                return s;
            }
    
            case 2:
            case 3:
            {
                // TODO: validate 2nd/3rd args
                if (!MP_OBJ_IS_TYPE(args[0], &mp_type_bytes)) {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "bytes expected"));
                }
                GET_STR_DATA_LEN(args[0], str_data, str_len);
                GET_STR_HASH(args[0], str_hash);
                mp_obj_str_t *o = mp_obj_new_str_of_type(&mp_type_str, NULL, str_len);
                o->data = str_data;
                o->hash = str_hash;
                return o;
            }
    
            default:
                nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "str takes at most 3 arguments"));
        }
    }
    
    STATIC mp_obj_t bytes_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const mp_obj_t *args) {
        if (n_args == 0) {
            return mp_const_empty_bytes;
        }
    
    #if MICROPY_CPYTHON_COMPAT
        if (n_kw != 0) {
            mp_arg_error_unimpl_kw();
        }
    #endif
    
        if (MP_OBJ_IS_STR(args[0])) {
            if (n_args < 2 || n_args > 3) {
                goto wrong_args;
            }
            GET_STR_DATA_LEN(args[0], str_data, str_len);
            GET_STR_HASH(args[0], str_hash);
            mp_obj_str_t *o = mp_obj_new_str_of_type(&mp_type_bytes, NULL, str_len);
            o->data = str_data;
            o->hash = str_hash;
            return o;
        }
    
        if (n_args > 1) {
            goto wrong_args;
        }
    
        if (MP_OBJ_IS_SMALL_INT(args[0])) {
            uint len = MP_OBJ_SMALL_INT_VALUE(args[0]);
            byte *data;
    
            mp_obj_t o = mp_obj_str_builder_start(&mp_type_bytes, len, &data);
            memset(data, 0, len);
            return mp_obj_str_builder_end(o);
        }
    
        int len;
        byte *data;
        vstr_t *vstr = NULL;
        mp_obj_t o = NULL;
        // Try to create array of exact len if initializer len is known
        mp_obj_t len_in = mp_obj_len_maybe(args[0]);
        if (len_in == MP_OBJ_NULL) {
            len = -1;
            vstr = vstr_new();
        } else {
            len = MP_OBJ_SMALL_INT_VALUE(len_in);
            o = mp_obj_str_builder_start(&mp_type_bytes, len, &data);
        }
    
        mp_obj_t iterable = mp_getiter(args[0]);
        mp_obj_t item;
        while ((item = mp_iternext(iterable)) != MP_OBJ_STOP_ITERATION) {
            if (len == -1) {
                vstr_add_char(vstr, MP_OBJ_SMALL_INT_VALUE(item));
            } else {
                *data++ = MP_OBJ_SMALL_INT_VALUE(item);
            }
        }
    
        if (len == -1) {
            vstr_shrink(vstr);
            // TODO: Optimize, borrow buffer from vstr
            len = vstr_len(vstr);
            o = mp_obj_str_builder_start(&mp_type_bytes, len, &data);
            memcpy(data, vstr_str(vstr), len);
            vstr_free(vstr);
        }
    
        return mp_obj_str_builder_end(o);
    
    wrong_args:
            nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "wrong number of arguments"));
    }
    
    // like strstr but with specified length and allows \0 bytes
    // TODO replace with something more efficient/standard
    STATIC const byte *find_subbytes(const byte *haystack, machine_uint_t hlen, const byte *needle, machine_uint_t nlen, machine_int_t direction) {
        if (hlen >= nlen) {
            machine_uint_t str_index, str_index_end;
            if (direction > 0) {
                str_index = 0;
                str_index_end = hlen - nlen;
            } else {
                str_index = hlen - nlen;
                str_index_end = 0;
            }
            for (;;) {
                if (memcmp(&haystack[str_index], needle, nlen) == 0) {
                    //found
                    return haystack + str_index;
                }
                if (str_index == str_index_end) {
                    //not found
                    break;
                }
                str_index += direction;
            }
        }
        return NULL;
    }
    
    STATIC mp_obj_t str_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
        GET_STR_DATA_LEN(lhs_in, lhs_data, lhs_len);
        mp_obj_type_t *lhs_type = mp_obj_get_type(lhs_in);
        mp_obj_type_t *rhs_type = mp_obj_get_type(rhs_in);
        switch (op) {
            case MP_BINARY_OP_ADD:
            case MP_BINARY_OP_INPLACE_ADD:
                if (lhs_type == rhs_type) {
                    // add 2 strings or bytes
    
                    GET_STR_DATA_LEN(rhs_in, rhs_data, rhs_len);
                    int alloc_len = lhs_len + rhs_len;
    
                    /* code for making qstr
                    byte *q_ptr;
                    byte *val = qstr_build_start(alloc_len, &q_ptr);
                    memcpy(val, lhs_data, lhs_len);
                    memcpy(val + lhs_len, rhs_data, rhs_len);
                    return MP_OBJ_NEW_QSTR(qstr_build_end(q_ptr));
                    */
    
                    // code for non-qstr
                    byte *data;
                    mp_obj_t s = mp_obj_str_builder_start(lhs_type, alloc_len, &data);
                    memcpy(data, lhs_data, lhs_len);
                    memcpy(data + lhs_len, rhs_data, rhs_len);
                    return mp_obj_str_builder_end(s);
                }
                break;
    
            case MP_BINARY_OP_IN:
                /* NOTE `a in b` is `b.__contains__(a)` */
                if (lhs_type == rhs_type) {
                    GET_STR_DATA_LEN(rhs_in, rhs_data, rhs_len);
                    return MP_BOOL(find_subbytes(lhs_data, lhs_len, rhs_data, rhs_len, 1) != NULL);
                }
                break;
    
            case MP_BINARY_OP_MULTIPLY: {
                if (!MP_OBJ_IS_SMALL_INT(rhs_in)) {
                    return MP_OBJ_NULL; // op not supported
                }
                int n = MP_OBJ_SMALL_INT_VALUE(rhs_in);
                byte *data;
                mp_obj_t s = mp_obj_str_builder_start(lhs_type, lhs_len * n, &data);
                mp_seq_multiply(lhs_data, sizeof(*lhs_data), lhs_len, n, data);
                return mp_obj_str_builder_end(s);
            }
    
            case MP_BINARY_OP_MODULO: {
                mp_obj_t *args;
                uint n_args;
                if (MP_OBJ_IS_TYPE(rhs_in, &mp_type_tuple)) {
                    // TODO: Support tuple subclasses?
                    mp_obj_tuple_get(rhs_in, &n_args, &args);
                } else {
                    args = &rhs_in;
                    n_args = 1;
                }
                return str_modulo_format(lhs_in, n_args, args);
            }
    
            //case MP_BINARY_OP_NOT_EQUAL: // This is never passed here
            case MP_BINARY_OP_EQUAL: // This will be passed only for bytes, str is dealt with in mp_obj_equal()
            case MP_BINARY_OP_LESS:
            case MP_BINARY_OP_LESS_EQUAL:
            case MP_BINARY_OP_MORE:
            case MP_BINARY_OP_MORE_EQUAL:
                if (lhs_type == rhs_type) {
                    GET_STR_DATA_LEN(rhs_in, rhs_data, rhs_len);
                    return MP_BOOL(mp_seq_cmp_bytes(op, lhs_data, lhs_len, rhs_data, rhs_len));
                }
                if (lhs_type == &mp_type_bytes) {
                    mp_buffer_info_t bufinfo;
                    if (!mp_get_buffer(rhs_in, &bufinfo, MP_BUFFER_READ)) {
                        goto uncomparable;
                    }
                    return MP_BOOL(mp_seq_cmp_bytes(op, lhs_data, lhs_len, bufinfo.buf, bufinfo.len));
                }
    uncomparable:
                if (op == MP_BINARY_OP_EQUAL) {
                    return mp_const_false;
                }
        }
    
        return MP_OBJ_NULL; // op not supported
    }
    
    STATIC mp_obj_t str_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
        mp_obj_type_t *type = mp_obj_get_type(self_in);
        GET_STR_DATA_LEN(self_in, self_data, self_len);
        if (value == MP_OBJ_SENTINEL) {
            // load
    #if MICROPY_PY_SLICE
            if (MP_OBJ_IS_TYPE(index, &mp_type_slice)) {
                mp_bound_slice_t slice;
                if (!mp_seq_get_fast_slice_indexes(self_len, index, &slice)) {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_NotImplementedError,
                        "Only slices with step=1 (aka None) are supported"));
                }
                return mp_obj_new_str_of_type(type, self_data + slice.start, slice.stop - slice.start);
            }
    #endif
            uint index_val = mp_get_index(type, self_len, index, false);
            if (type == &mp_type_bytes) {
                return MP_OBJ_NEW_SMALL_INT((mp_small_int_t)self_data[index_val]);
            } else {
                return mp_obj_new_str((char*)self_data + index_val, 1, true);
            }
        } else {
            return MP_OBJ_NULL; // op not supported
        }
    }
    
    STATIC mp_obj_t str_join(mp_obj_t self_in, mp_obj_t arg) {
        assert(is_str_or_bytes(self_in));
        const mp_obj_type_t *self_type = mp_obj_get_type(self_in);
    
        // get separation string
        GET_STR_DATA_LEN(self_in, sep_str, sep_len);
    
        // process args
        uint seq_len;
        mp_obj_t *seq_items;
        if (MP_OBJ_IS_TYPE(arg, &mp_type_tuple)) {
            mp_obj_tuple_get(arg, &seq_len, &seq_items);
        } else {
            if (!MP_OBJ_IS_TYPE(arg, &mp_type_list)) {
                // arg is not a list, try to convert it to one
                // TODO: Try to optimize?
                arg = mp_type_list.make_new((mp_obj_t)&mp_type_list, 1, 0, &arg);
            }
            mp_obj_list_get(arg, &seq_len, &seq_items);
        }
    
        // count required length
        int required_len = 0;
        for (int i = 0; i < seq_len; i++) {
            if (mp_obj_get_type(seq_items[i]) != self_type) {
                nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError,
                    "join expects a list of str/bytes objects consistent with self object"));
            }
            if (i > 0) {
                required_len += sep_len;
            }
            GET_STR_LEN(seq_items[i], l);
            required_len += l;
        }
    
        // make joined string
        byte *data;
        mp_obj_t joined_str = mp_obj_str_builder_start(self_type, required_len, &data);
        for (int i = 0; i < seq_len; i++) {
            if (i > 0) {
                memcpy(data, sep_str, sep_len);
                data += sep_len;
            }
            GET_STR_DATA_LEN(seq_items[i], s, l);
            memcpy(data, s, l);
            data += l;
        }
    
        // return joined string
        return mp_obj_str_builder_end(joined_str);
    }
    
    #define is_ws(c) ((c) == ' ' || (c) == '\t')
    
    STATIC mp_obj_t str_split(uint n_args, const mp_obj_t *args) {
        const mp_obj_type_t *self_type = mp_obj_get_type(args[0]);
        machine_int_t splits = -1;
        mp_obj_t sep = mp_const_none;
        if (n_args > 1) {
            sep = args[1];
            if (n_args > 2) {
                splits = mp_obj_get_int(args[2]);
            }
        }
    
        mp_obj_t res = mp_obj_new_list(0, NULL);
        GET_STR_DATA_LEN(args[0], s, len);
        const byte *top = s + len;
    
        if (sep == mp_const_none) {
            // sep not given, so separate on whitespace
    
            // Initial whitespace is not counted as split, so we pre-do it
            while (s < top && is_ws(*s)) s++;
            while (s < top && splits != 0) {
                const byte *start = s;
                while (s < top && !is_ws(*s)) s++;
                mp_obj_list_append(res, mp_obj_new_str_of_type(self_type, start, s - start));
                if (s >= top) {
                    break;
                }
                while (s < top && is_ws(*s)) s++;
                if (splits > 0) {
                    splits--;
                }
            }
    
            if (s < top) {
                mp_obj_list_append(res, mp_obj_new_str_of_type(self_type, s, top - s));
            }
    
        } else {
            // sep given
    
            uint sep_len;
            const char *sep_str = mp_obj_str_get_data(sep, &sep_len);
    
            if (sep_len == 0) {
                nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "empty separator"));
            }
    
            for (;;) {
                const byte *start = s;
                for (;;) {
                    if (splits == 0 || s + sep_len > top) {
                        s = top;
                        break;
                    } else if (memcmp(s, sep_str, sep_len) == 0) {
                        break;
                    }
                    s++;
                }
                mp_obj_list_append(res, mp_obj_new_str_of_type(self_type, start, s - start));
                if (s >= top) {
                    break;
                }
                s += sep_len;
                if (splits > 0) {
                    splits--;
                }
            }
        }
    
        return res;
    }
    
    STATIC mp_obj_t str_rsplit(uint n_args, const mp_obj_t *args) {
        if (n_args < 3) {
            // If we don't have split limit, it doesn't matter from which side
            // we split.
            return str_split(n_args, args);
        }
        const mp_obj_type_t *self_type = mp_obj_get_type(args[0]);
        mp_obj_t sep = args[1];
        GET_STR_DATA_LEN(args[0], s, len);
    
        machine_int_t splits = mp_obj_get_int(args[2]);
        machine_int_t org_splits = splits;
        // Preallocate list to the max expected # of elements, as we
        // will fill it from the end.
        mp_obj_list_t *res = mp_obj_new_list(splits + 1, NULL);
        int idx = splits;
    
        if (sep == mp_const_none) {
            // TODO
            assert(0);
        } else {
            uint sep_len;
            const char *sep_str = mp_obj_str_get_data(sep, &sep_len);
    
            if (sep_len == 0) {
                nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "empty separator"));
            }
    
            const byte *beg = s;
            const byte *last = s + len;
            for (;;) {
                s = last - sep_len;
                for (;;) {
                    if (splits == 0 || s < beg) {
                        break;
                    } else if (memcmp(s, sep_str, sep_len) == 0) {
                        break;
                    }
                    s--;
                }
                if (s < beg || splits == 0) {
                    res->items[idx] = mp_obj_new_str_of_type(self_type, beg, last - beg);
                    break;
                }
                res->items[idx--] = mp_obj_new_str_of_type(self_type, s + sep_len, last - s - sep_len);
                last = s;
                if (splits > 0) {
                    splits--;
                }
            }
            if (idx != 0) {
                // We split less parts than split limit, now go cleanup surplus
                int used = org_splits + 1 - idx;
                memcpy(res->items, &res->items[idx], used * sizeof(mp_obj_t));
                mp_seq_clear(res->items, used, res->alloc, sizeof(*res->items));
                res->len = used;
            }
        }
    
        return res;
    }
    
    
    STATIC mp_obj_t str_finder(uint n_args, const mp_obj_t *args, machine_int_t direction, bool is_index) {
        assert(2 <= n_args && n_args <= 4);
        assert(MP_OBJ_IS_STR(args[0]));
        assert(MP_OBJ_IS_STR(args[1]));
    
        GET_STR_DATA_LEN(args[0], haystack, haystack_len);
        GET_STR_DATA_LEN(args[1], needle, needle_len);
    
        machine_uint_t start = 0;
        machine_uint_t end = haystack_len;
        if (n_args >= 3 && args[2] != mp_const_none) {
            start = mp_get_index(&mp_type_str, haystack_len, args[2], true);
        }
        if (n_args >= 4 && args[3] != mp_const_none) {
            end = mp_get_index(&mp_type_str, haystack_len, args[3], true);
        }
    
        const byte *p = find_subbytes(haystack + start, end - start, needle, needle_len, direction);
        if (p == NULL) {
            // not found
            if (is_index) {
                nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "substring not found"));
            } else {
                return MP_OBJ_NEW_SMALL_INT(-1);
            }
        } else {
            // found
            return MP_OBJ_NEW_SMALL_INT(p - haystack);
        }
    }
    
    STATIC mp_obj_t str_find(uint n_args, const mp_obj_t *args) {
        return str_finder(n_args, args, 1, false);
    }
    
    STATIC mp_obj_t str_rfind(uint n_args, const mp_obj_t *args) {
        return str_finder(n_args, args, -1, false);
    }
    
    STATIC mp_obj_t str_index(uint n_args, const mp_obj_t *args) {
        return str_finder(n_args, args, 1, true);
    }
    
    STATIC mp_obj_t str_rindex(uint n_args, const mp_obj_t *args) {
        return str_finder(n_args, args, -1, true);
    }
    
    // TODO: (Much) more variety in args
    STATIC mp_obj_t str_startswith(uint n_args, const mp_obj_t *args) {
        GET_STR_DATA_LEN(args[0], str, str_len);
        GET_STR_DATA_LEN(args[1], prefix, prefix_len);
        uint index_val = 0;
        if (n_args > 2) {
            index_val = mp_get_index(&mp_type_str, str_len, args[2], true);
        }
        if (prefix_len + index_val > str_len) {
            return mp_const_false;
        }
        return MP_BOOL(memcmp(str + index_val, prefix, prefix_len) == 0);
    }
    
    STATIC mp_obj_t str_endswith(uint n_args, const mp_obj_t *args) {
        GET_STR_DATA_LEN(args[0], str, str_len);
        GET_STR_DATA_LEN(args[1], suffix, suffix_len);
        assert(n_args == 2);
    
        if (suffix_len > str_len) {
            return mp_const_false;
        }
        return MP_BOOL(memcmp(str + (str_len - suffix_len), suffix, suffix_len) == 0);
    }
    
    enum { LSTRIP, RSTRIP, STRIP };
    
    STATIC mp_obj_t str_uni_strip(int type, uint n_args, const mp_obj_t *args) {
        assert(1 <= n_args && n_args <= 2);
        assert(is_str_or_bytes(args[0]));
        const mp_obj_type_t *self_type = mp_obj_get_type(args[0]);
    
        const byte *chars_to_del;
        uint chars_to_del_len;
        static const byte whitespace[] = " \t\n\r\v\f";
    
        if (n_args == 1) {
            chars_to_del = whitespace;
            chars_to_del_len = sizeof(whitespace);
        } else {
            if (mp_obj_get_type(args[1]) != self_type) {
                arg_type_mixup();
            }
            GET_STR_DATA_LEN(args[1], s, l);
            chars_to_del = s;
            chars_to_del_len = l;
        }
    
        GET_STR_DATA_LEN(args[0], orig_str, orig_str_len);
    
        machine_uint_t first_good_char_pos = 0;
        bool first_good_char_pos_set = false;
        machine_uint_t last_good_char_pos = 0;
        machine_uint_t i = 0;
        machine_int_t delta = 1;
        if (type == RSTRIP) {
            i = orig_str_len - 1;
            delta = -1;
        }
        for (machine_uint_t len = orig_str_len; len > 0; len--) {
            if (find_subbytes(chars_to_del, chars_to_del_len, &orig_str[i], 1, 1) == NULL) {
                if (!first_good_char_pos_set) {
                    first_good_char_pos_set = true;
                    first_good_char_pos = i;
                    if (type == LSTRIP) {
                        last_good_char_pos = orig_str_len - 1;
                        break;
                    } else if (type == RSTRIP) {
                        first_good_char_pos = 0;
                        last_good_char_pos = i;
                        break;
                    }
                }
                last_good_char_pos = i;
            }
            i += delta;
        }
    
        if (!first_good_char_pos_set) {
            // string is all whitespace, return ''
            return MP_OBJ_NEW_QSTR(MP_QSTR_);
        }
    
        assert(last_good_char_pos >= first_good_char_pos);
        //+1 to accomodate the last character
        machine_uint_t stripped_len = last_good_char_pos - first_good_char_pos + 1;
        if (stripped_len == orig_str_len) {
            // If nothing was stripped, don't bother to dup original string
            // TODO: watch out for this case when we'll get to bytearray.strip()
            assert(first_good_char_pos == 0);
            return args[0];
        }
        return mp_obj_new_str_of_type(self_type, orig_str + first_good_char_pos, stripped_len);
    }
    
    STATIC mp_obj_t str_strip(uint n_args, const mp_obj_t *args) {
        return str_uni_strip(STRIP, n_args, args);
    }
    
    STATIC mp_obj_t str_lstrip(uint n_args, const mp_obj_t *args) {
        return str_uni_strip(LSTRIP, n_args, args);
    }
    
    STATIC mp_obj_t str_rstrip(uint n_args, const mp_obj_t *args) {
        return str_uni_strip(RSTRIP, n_args, args);
    }
    
    // Takes an int arg, but only parses unsigned numbers, and only changes
    // *num if at least one digit was parsed.
    static int str_to_int(const char *str, int *num) {
        const char *s = str;
        if (unichar_isdigit(*s)) {
            *num = 0;
            do {
                *num = *num * 10 + (*s - '0');
                s++;
            }
            while (unichar_isdigit(*s));
        }
        return s - str;
    }
    
    static bool isalignment(char ch) {
        return ch && strchr("<>=^", ch) != NULL;
    }
    
    static bool istype(char ch) {
        return ch && strchr("bcdeEfFgGnosxX%", ch) != NULL;
    }
    
    static bool arg_looks_integer(mp_obj_t arg) {
        return MP_OBJ_IS_TYPE(arg, &mp_type_bool) || MP_OBJ_IS_INT(arg);
    }
    
    static bool arg_looks_numeric(mp_obj_t arg) {
        return arg_looks_integer(arg)
    #if MICROPY_ENABLE_FLOAT
            || MP_OBJ_IS_TYPE(arg, &mp_type_float)
    #endif
        ;
    }
    
    static mp_obj_t arg_as_int(mp_obj_t arg) {
    #if MICROPY_ENABLE_FLOAT
        if (MP_OBJ_IS_TYPE(arg, &mp_type_float)) {
    
            // TODO: Needs a way to construct an mpz integer from a float
    
            mp_small_int_t num = mp_obj_get_float(arg);
            return MP_OBJ_NEW_SMALL_INT(num);
        }
    #endif
        return arg;
    }
    
    mp_obj_t mp_obj_str_format(uint n_args, const mp_obj_t *args) {
        assert(MP_OBJ_IS_STR(args[0]));
    
        GET_STR_DATA_LEN(args[0], str, len);
        int arg_i = 0;
        vstr_t *vstr = vstr_new();
        pfenv_t pfenv_vstr;
        pfenv_vstr.data = vstr;
        pfenv_vstr.print_strn = pfenv_vstr_add_strn;
    
        for (const byte *top = str + len; str < top; str++) {
            if (*str == '}') {
                str++;
                if (str < top && *str == '}') {
                    vstr_add_char(vstr, '}');
                    continue;
                }
                nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Single '}' encountered in format string"));
            }
            if (*str != '{') {
                vstr_add_char(vstr, *str);
                continue;
            }
    
            str++;
            if (str < top && *str == '{') {
                vstr_add_char(vstr, '{');
                continue;
            }
    
            // replacement_field ::=  "{" [field_name] ["!" conversion] [":" format_spec] "}"
    
            vstr_t *field_name = NULL;
            char conversion = '\0';
            vstr_t *format_spec = NULL;
    
            if (str < top && *str != '}' && *str != '!' && *str != ':') {
                field_name = vstr_new();
                while (str < top && *str != '}' && *str != '!' && *str != ':') {
                    vstr_add_char(field_name, *str++);
                }
                vstr_add_char(field_name, '\0');
            }
    
            // conversion ::=  "r" | "s"
    
            if (str < top && *str == '!') {
                str++;
                if (str < top && (*str == 'r' || *str == 's')) {
                    conversion = *str++;
                } else {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "end of format while looking for conversion specifier"));
                }
            }
    
            if (str < top && *str == ':') {
                str++;
                // {:} is the same as {}, which is the same as {!s}
                // This makes a difference when passing in a True or False
                // '{}'.format(True) returns 'True'
                // '{:d}'.format(True) returns '1'
                // So we treat {:} as {} and this later gets treated to be {!s}
                if (*str != '}') {
                    format_spec = vstr_new(); 
                    while (str < top && *str != '}') {
                        vstr_add_char(format_spec, *str++);
                    }
                    vstr_add_char(format_spec, '\0');
                }
            }
            if (str >= top) {
                nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "unmatched '{' in format"));
            }
            if (*str != '}') {
                nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "expected ':' after format specifier"));
            }
    
            mp_obj_t arg = mp_const_none;
    
            if (field_name) {
                if (arg_i > 0) {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "cannot switch from automatic field numbering to manual field specification"));
                }
                int index = 0;
                if (str_to_int(vstr_str(field_name), &index) != vstr_len(field_name) - 1) {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_KeyError, "attributes not supported yet"));
                }
                if (index >= n_args - 1) {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_IndexError, "tuple index out of range"));
                }
                arg = args[index + 1];
                arg_i = -1;
                vstr_free(field_name);
                field_name = NULL;
            } else {
                if (arg_i < 0) {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "cannot switch from manual field specification to automatic field numbering"));
                }
                if (arg_i >= n_args - 1) {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_IndexError, "tuple index out of range"));
                }
                arg = args[arg_i + 1];
                arg_i++;
            }
            if (!format_spec && !conversion) {
                conversion = 's';
            }
            if (conversion) {
                mp_print_kind_t print_kind;
                if (conversion == 's') {
                    print_kind = PRINT_STR;
                } else if (conversion == 'r') {
                    print_kind = PRINT_REPR;
                } else {
                    nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "Unknown conversion specifier %c", conversion));
                }
                vstr_t *arg_vstr = vstr_new();
                mp_obj_print_helper((void (*)(void*, const char*, ...))vstr_printf, arg_vstr, arg, print_kind);
                arg = mp_obj_new_str(vstr_str(arg_vstr), vstr_len(arg_vstr), false);
                vstr_free(arg_vstr);
            }
    
            char sign = '\0';
            char fill = '\0';
            char align = '\0';
            int width = -1;
            int precision = -1;
            char type = '\0';
            int flags = 0;
    
            if (format_spec) {
                // The format specifier (from http://docs.python.org/2/library/string.html#formatspec)
                //
                // [[fill]align][sign][#][0][width][,][.precision][type]
                // fill        ::=  <any character>
                // align       ::=  "<" | ">" | "=" | "^"
                // sign        ::=  "+" | "-" | " "
                // width       ::=  integer
                // precision   ::=  integer
                // type        ::=  "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"
    
                const char *s = vstr_str(format_spec);
                if (isalignment(*s)) {
                    align = *s++;
                } else if (*s && isalignment(s[1])) {
                    fill = *s++;
                    align = *s++;
                }
                if (*s == '+' || *s == '-' || *s == ' ') {
                    if (*s == '+') {
                        flags |= PF_FLAG_SHOW_SIGN;
                    } else if (*s == ' ') {
                        flags |= PF_FLAG_SPACE_SIGN;
                    }
                    sign = *s++;
                }
                if (*s == '#') {
                    flags |= PF_FLAG_SHOW_PREFIX;
                    s++;
                }
                if (*s == '0') {
                    if (!align) {
                        align = '=';
                    }
                    if (!fill) {
                        fill = '0';
                    }
                }
                s += str_to_int(s, &width);
                if (*s == ',') {
                    flags |= PF_FLAG_SHOW_COMMA;
                    s++;
                }
                if (*s == '.') {
                    s++;
                    s += str_to_int(s, &precision);
                }
                if (istype(*s)) {
                    type = *s++;
                }
                if (*s) {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_KeyError, "Invalid conversion specification"));
                }
                vstr_free(format_spec);
                format_spec = NULL;
            }
            if (!align) {
                if (arg_looks_numeric(arg)) {
                    align = '>';
                } else {
                    align = '<';
                }
            }
            if (!fill) {
                fill = ' ';
            }
    
            if (sign) {
                if (type == 's') {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Sign not allowed in string format specifier"));
                }
                if (type == 'c') {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Sign not allowed with integer format specifier 'c'"));
                }
            } else {
                sign = '-';
            }
    
            switch (align) {
                case '<': flags |= PF_FLAG_LEFT_ADJUST;     break;
                case '=': flags |= PF_FLAG_PAD_AFTER_SIGN;  break;
                case '^': flags |= PF_FLAG_CENTER_ADJUST;   break;
            }
    
            if (arg_looks_integer(arg)) {
                switch (type) {
                    case 'b':
                        pfenv_print_mp_int(&pfenv_vstr, arg, 1, 2, 'a', flags, fill, width);
                        continue;
    
                    case 'c':
                    {
                        char ch = mp_obj_get_int(arg);
                        pfenv_print_strn(&pfenv_vstr, &ch, 1, flags, fill, width);
                        continue;
                    }
    
                    case '\0':  // No explicit format type implies 'd'
                    case 'n':   // I don't think we support locales in uPy so use 'd'
                    case 'd':
                        pfenv_print_mp_int(&pfenv_vstr, arg, 1, 10, 'a', flags, fill, width);
                        continue;
    
                    case 'o':
                        if (flags & PF_FLAG_SHOW_PREFIX) {
                            flags |= PF_FLAG_SHOW_OCTAL_LETTER;
                        }
    
                        pfenv_print_mp_int(&pfenv_vstr, arg, 1, 8, 'a', flags, fill, width);
                        continue;
    
                    case 'x':
                        pfenv_print_mp_int(&pfenv_vstr, arg, 1, 16, 'a', flags, fill, width);
                        continue;
    
                    case 'X':
                        pfenv_print_mp_int(&pfenv_vstr, arg, 1, 16, 'A', flags, fill, width);
                        continue;
    
                    case 'e':
                    case 'E':
                    case 'f':
                    case 'F':
                    case 'g':
                    case 'G':
                    case '%':
                        // The floating point formatters all work with anything that
                        // looks like an integer
                        break;
    
                    default:
                        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError,
                            "Unknown format code '%c' for object of type '%s'", type, mp_obj_get_type_str(arg)));
                }
            }
    
            // NOTE: no else here. We need the e, f, g etc formats for integer
            //       arguments (from above if) to take this if.
            if (arg_looks_numeric(arg)) {
                if (!type) {
    
                    // Even though the docs say that an unspecified type is the same
                    // as 'g', there is one subtle difference, when the exponent
                    // is one less than the precision.
                    //  
                    // '{:10.1}'.format(0.0) ==> '0e+00'
                    // '{:10.1g}'.format(0.0) ==> '0'
                    //
                    // TODO: Figure out how to deal with this.
                    //
                    // A proper solution would involve adding a special flag
                    // or something to format_float, and create a format_double
                    // to deal with doubles. In order to fix this when using
                    // sprintf, we'd need to use the e format and tweak the
                    // returned result to strip trailing zeros like the g format
                    // does.
                    //
                    // {:10.3} and {:10.2e} with 1.23e2 both produce 1.23e+02
                    // but with 1.e2 you get 1e+02 and 1.00e+02
                    //
                    // Stripping the trailing 0's (like g) does would make the
                    // e format give us the right format.
                    //
                    // CPython sources say:
                    //   Omitted type specifier.  Behaves in the same way as repr(x)
                    //   and str(x) if no precision is given, else like 'g', but with
                    //   at least one digit after the decimal point. */
    
                    type = 'g';
                }
                if (type == 'n') {
                    type = 'g';
                }
    
                flags |= PF_FLAG_PAD_NAN_INF; // '{:06e}'.format(float('-inf')) should give '-00inf'
                switch (type) {
    #if MICROPY_ENABLE_FLOAT
                    case 'e':
                    case 'E':
                    case 'f':
                    case 'F':
                    case 'g':
                    case 'G':
                        pfenv_print_float(&pfenv_vstr, mp_obj_get_float(arg), type, flags, fill, width, precision); 
                        break;
    
                    case '%':
                        flags |= PF_FLAG_ADD_PERCENT;
                        pfenv_print_float(&pfenv_vstr, mp_obj_get_float(arg) * 100.0F, 'f', flags, fill, width, precision);
                        break;
    #endif
    
                    default:
                        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError,
                            "Unknown format code '%c' for object of type 'float'",
                            type, mp_obj_get_type_str(arg)));
                }
            } else {
                // arg doesn't look like a number
    
                if (align == '=') {
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "'=' alignment not allowed in string format specifier"));
                }
    
                switch (type) {
                    case '\0':
                        mp_obj_print_helper((void (*)(void*, const char*, ...))vstr_printf, vstr, arg, PRINT_STR);
                        break;
    
                    case 's':
                    {
                        uint len;
                        const char *s = mp_obj_str_get_data(arg, &len);
                        if (precision < 0) {
                            precision = len;
                        }
                        if (len > precision) {
                            len = precision;
                        }
                        pfenv_print_strn(&pfenv_vstr, s, len, flags, fill, width);
                        break;
                    }
    
                    default:
                        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError,
                            "Unknown format code '%c' for object of type 'str'",
                            type, mp_obj_get_type_str(arg)));
                }
            }
        }
    
        mp_obj_t s = mp_obj_new_str(vstr->buf, vstr->len, false);
        vstr_free(vstr);
        return s;
    }
    
    STATIC mp_obj_t str_modulo_format(mp_obj_t pattern, uint n_args, const mp_obj_t *args) {
        assert(MP_OBJ_IS_STR(pattern));
    
        GET_STR_DATA_LEN(pattern, str, len);
        const byte *start_str = str;
        int arg_i = 0;
        vstr_t *vstr = vstr_new();
        pfenv_t pfenv_vstr;
        pfenv_vstr.data = vstr;
        pfenv_vstr.print_strn = pfenv_vstr_add_strn;
    
        for (const byte *top = str + len; str < top; str++) {
            if (*str != '%') {
                vstr_add_char(vstr, *str);
                continue;
            }
            if (++str >= top) {
                break;
            }
            if (*str == '%') {
                vstr_add_char(vstr, '%');
                continue;
            }
            if (arg_i >= n_args) {
                nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "not enough arguments for format string"));
            }
            int flags = 0;
            char fill = ' ';
            bool alt = false;
            while (str < top) {
                if (*str == '-')      flags |= PF_FLAG_LEFT_ADJUST;
                else if (*str == '+') flags |= PF_FLAG_SHOW_SIGN;
                else if (*str == ' ') flags |= PF_FLAG_SPACE_SIGN;
                else if (*str == '#') alt = true;
                else if (*str == '0') {
                    flags |= PF_FLAG_PAD_AFTER_SIGN;
                    fill = '0';
                } else break;
                str++;
            }
            // parse width, if it exists
            int width = 0; 
            if (str < top) {
                if (*str == '*') {
                    width = mp_obj_get_int(args[arg_i++]);
                    str++;
                } else {
                    for (; str < top && '0' <= *str && *str <= '9'; str++) {
                        width = width * 10 + *str - '0';
                    }
                }
            }
            int prec = -1;
            if (str < top && *str == '.') {
                if (++str < top) {
                    if (*str == '*') {
                        prec = mp_obj_get_int(args[arg_i++]);
                        str++;
                    } else {
                        prec = 0;
                        for (; str < top && '0' <= *str && *str <= '9'; str++) {
                            prec = prec * 10 + *str - '0';
                        }
                    }
                }
            }
    
            if (str >= top) {
                nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "incomplete format"));
            }
            mp_obj_t arg = args[arg_i];
            switch (*str) {
                case 'c':
                    if (MP_OBJ_IS_STR(arg)) {
                        uint len;
                        const char *s = mp_obj_str_get_data(arg, &len);
                        if (len != 1) {
                            nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "%c requires int or char")); 
                            break;
                        }
                        pfenv_print_strn(&pfenv_vstr, s, 1, flags, ' ', width);
                        break;
                    }
                    if (arg_looks_integer(arg)) {
                        char ch = mp_obj_get_int(arg);
                        pfenv_print_strn(&pfenv_vstr, &ch, 1, flags, ' ', width);
                        break;
                    }
    #if MICROPY_ENABLE_FLOAT
                    // This is what CPython reports, so we report the same.
                    if (MP_OBJ_IS_TYPE(arg, &mp_type_float)) {
                        nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "integer argument expected, got float")); 
    
                    }
    #endif
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "an integer is required")); 
                    break; 
    
                case 'd':
                case 'i':
                case 'u':
                    pfenv_print_mp_int(&pfenv_vstr, arg_as_int(arg), 1, 10, 'a', flags, fill, width);
                    break;
    
    #if MICROPY_ENABLE_FLOAT
                case 'e':
                case 'E':
                case 'f':
                case 'F':
                case 'g':
                case 'G':
                    pfenv_print_float(&pfenv_vstr, mp_obj_get_float(arg), *str, flags, fill, width, prec);
                    break;
    #endif
    
                case 'o':
                    if (alt) {
                        flags |= (PF_FLAG_SHOW_PREFIX | PF_FLAG_SHOW_OCTAL_LETTER);
                    }
                    pfenv_print_mp_int(&pfenv_vstr, arg_as_int(arg), 1, 8, 'a', flags, fill, width); 
                    break;
    
                case 'r':
                case 's':
                {
                    vstr_t *arg_vstr = vstr_new();
                    mp_obj_print_helper((void (*)(void*, const char*, ...))vstr_printf,
                                        arg_vstr, arg, *str == 'r' ? PRINT_REPR : PRINT_STR);
                    uint len = vstr_len(arg_vstr);
                    if (prec < 0) {
                        prec = len;
                    }
                    if (len > prec) {
                        len = prec;
                    }
                    pfenv_print_strn(&pfenv_vstr, vstr_str(arg_vstr), len, flags, ' ', width);
                    vstr_free(arg_vstr);
                    break;
                }
    
                case 'x':
                    if (alt) {
                        flags |= PF_FLAG_SHOW_PREFIX;
                    }
                    pfenv_print_mp_int(&pfenv_vstr, arg_as_int(arg), 1, 16, 'a', flags, fill, width);
                    break;
    
                case 'X':
                    if (alt) {
                        flags |= PF_FLAG_SHOW_PREFIX;
                    }
                    pfenv_print_mp_int(&pfenv_vstr, arg_as_int(arg), 1, 16, 'A', flags, fill, width);
                    break;
    
                default:
                    nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError,
                        "unsupported format character '%c' (0x%x) at index %d",
                        *str, *str, str - start_str));
            }
            arg_i++;
        }
    
        if (arg_i != n_args) {
            nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "not all arguments converted during string formatting"));
        }
    
        mp_obj_t s = mp_obj_new_str(vstr->buf, vstr->len, false);
        vstr_free(vstr);
        return s;
    }
    
    STATIC mp_obj_t str_replace(uint n_args, const mp_obj_t *args) {
        assert(MP_OBJ_IS_STR(args[0]));
    
        machine_int_t max_rep = -1;
        if (n_args == 4) {
            max_rep = mp_obj_get_int(args[3]);
            if (max_rep == 0) {
                return args[0];
            } else if (max_rep < 0) {
                max_rep = -1;
            }
        }
    
        // if max_rep is still -1 by this point we will need to do all possible replacements
    
        // check argument types
    
        if (!MP_OBJ_IS_STR(args[1])) {
            bad_implicit_conversion(args[1]);
        }
    
        if (!MP_OBJ_IS_STR(args[2])) {
            bad_implicit_conversion(args[2]);
        }
    
        // extract string data
    
        GET_STR_DATA_LEN(args[0], str, str_len);
        GET_STR_DATA_LEN(args[1], old, old_len);
        GET_STR_DATA_LEN(args[2], new, new_len);
    
        // old won't exist in str if it's longer, so nothing to replace
        if (old_len > str_len) {
            return args[0];
        }
    
        // data for the replaced string
        byte *data = NULL;
        mp_obj_t replaced_str = MP_OBJ_NULL;
    
        // do 2 passes over the string:
        //   first pass computes the required length of the replaced string
        //   second pass does the replacements
        for (;;) {
            machine_uint_t replaced_str_index = 0;
            machine_uint_t num_replacements_done = 0;
            const byte *old_occurrence;
            const byte *offset_ptr = str;
            machine_uint_t str_len_remain = str_len;
            if (old_len == 0) {
                // if old_str is empty, copy new_str to start of replaced string
                // copy the replacement string
                if (data != NULL) {
                    memcpy(data, new, new_len);
                }
                replaced_str_index += new_len;
                num_replacements_done++;
            }
            while (num_replacements_done != max_rep && str_len_remain > 0 && (old_occurrence = find_subbytes(offset_ptr, str_len_remain, old, old_len, 1)) != NULL) {
                if (old_len == 0) {
                    old_occurrence += 1;
                }
                // copy from just after end of last occurrence of to-be-replaced string to right before start of next occurrence
                if (data != NULL) {
                    memcpy(data + replaced_str_index, offset_ptr, old_occurrence - offset_ptr);
                }
                replaced_str_index += old_occurrence - offset_ptr;
                // copy the replacement string
                if (data != NULL) {
                    memcpy(data + replaced_str_index, new, new_len);
                }
                replaced_str_index += new_len;
                offset_ptr = old_occurrence + old_len;
                str_len_remain = str + str_len - offset_ptr;
                num_replacements_done++;
            }
    
            // copy from just after end of last occurrence of to-be-replaced string to end of old string
            if (data != NULL) {
                memcpy(data + replaced_str_index, offset_ptr, str_len_remain);
            }
            replaced_str_index += str_len_remain;
    
            if (data == NULL) {
                // first pass
                if (num_replacements_done == 0) {
                    // no substr found, return original string
                    return args[0];
                } else {
                    // substr found, allocate new string
                    replaced_str = mp_obj_str_builder_start(mp_obj_get_type(args[0]), replaced_str_index, &data);
                    assert(data != NULL);
                }
            } else {
                // second pass, we are done
                break;
            }
        }
    
        return mp_obj_str_builder_end(replaced_str);
    }
    
    STATIC mp_obj_t str_count(uint n_args, const mp_obj_t *args) {
        assert(2 <= n_args && n_args <= 4);
        assert(MP_OBJ_IS_STR(args[0]));
        assert(MP_OBJ_IS_STR(args[1]));
    
        GET_STR_DATA_LEN(args[0], haystack, haystack_len);
        GET_STR_DATA_LEN(args[1], needle, needle_len);
    
        machine_uint_t start = 0;
        machine_uint_t end = haystack_len;
        if (n_args >= 3 && args[2] != mp_const_none) {
            start = mp_get_index(&mp_type_str, haystack_len, args[2], true);
        }
        if (n_args >= 4 && args[3] != mp_const_none) {
            end = mp_get_index(&mp_type_str, haystack_len, args[3], true);
        }
    
        // if needle_len is zero then we count each gap between characters as an occurrence
        if (needle_len == 0) {
            return MP_OBJ_NEW_SMALL_INT(end - start + 1);
        }
    
        // count the occurrences
        machine_int_t num_occurrences = 0;
        for (machine_uint_t haystack_index = start; haystack_index + needle_len <= end; haystack_index++) {
            if (memcmp(&haystack[haystack_index], needle, needle_len) == 0) {
                num_occurrences++;
                haystack_index += needle_len - 1;
            }
        }
    
        return MP_OBJ_NEW_SMALL_INT(num_occurrences);
    }
    
    STATIC mp_obj_t str_partitioner(mp_obj_t self_in, mp_obj_t arg, machine_int_t direction) {
        if (!is_str_or_bytes(self_in)) {
            assert(0);
        }
        mp_obj_type_t *self_type = mp_obj_get_type(self_in);
        if (self_type != mp_obj_get_type(arg)) {
            arg_type_mixup();
        }
    
        GET_STR_DATA_LEN(self_in, str, str_len);
        GET_STR_DATA_LEN(arg, sep, sep_len);
    
        if (sep_len == 0) {
            nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "empty separator"));
        }
    
        mp_obj_t result[] = {MP_OBJ_NEW_QSTR(MP_QSTR_), MP_OBJ_NEW_QSTR(MP_QSTR_), MP_OBJ_NEW_QSTR(MP_QSTR_)};
    
        if (direction > 0) {
            result[0] = self_in;
        } else {
            result[2] = self_in;
        }
    
        const byte *position_ptr = find_subbytes(str, str_len, sep, sep_len, direction);
        if (position_ptr != NULL) {
            machine_uint_t position = position_ptr - str;
            result[0] = mp_obj_new_str_of_type(self_type, str, position);
            result[1] = arg;
            result[2] = mp_obj_new_str_of_type(self_type, str + position + sep_len, str_len - position - sep_len);
        }
    
        return mp_obj_new_tuple(3, result);
    }
    
    STATIC mp_obj_t str_partition(mp_obj_t self_in, mp_obj_t arg) {
        return str_partitioner(self_in, arg, 1);
    }
    
    STATIC mp_obj_t str_rpartition(mp_obj_t self_in, mp_obj_t arg) {
        return str_partitioner(self_in, arg, -1);
    }
    
    enum { CASE_UPPER, CASE_LOWER };
    
    // Supposedly not too critical operations, so optimize for code size
    STATIC mp_obj_t str_caseconv(int op, mp_obj_t self_in) {
        GET_STR_DATA_LEN(self_in, self_data, self_len);
        byte *data;
        mp_obj_t s = mp_obj_str_builder_start(mp_obj_get_type(self_in), self_len, &data);
        for (int i = 0; i < self_len; i++) {
            if (op == CASE_UPPER) {
                *data++ = unichar_toupper(*self_data++);
            } else {
                *data++ = unichar_tolower(*self_data++);
            }
        }
        *data = 0;
        return mp_obj_str_builder_end(s);
    }
    
    STATIC mp_obj_t str_lower(mp_obj_t self_in) {
        return str_caseconv(CASE_LOWER, self_in);
    }
    
    STATIC mp_obj_t str_upper(mp_obj_t self_in) {
        return str_caseconv(CASE_UPPER, self_in);
    }
    
    enum { IS_SPACE, IS_ALPHA, IS_DIGIT, IS_UPPER, IS_LOWER };
    
    STATIC mp_obj_t str_uni_istype(int type, mp_obj_t self_in) {
        GET_STR_DATA_LEN(self_in, self_data, self_len);
        
        if (self_len == 0) {
            return mp_const_false; // default to False for empty str
        }
            
        typedef bool (*check_function)(unichar);
        check_function f;
        
        if (type != IS_UPPER && type != IS_LOWER) {
            switch (type) {
                case IS_SPACE: f = &unichar_isspace; break;
                case IS_ALPHA: f = &unichar_isalpha; break;
                case IS_DIGIT: f = &unichar_isdigit; break;
                default:
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "unknown type provided for str_uni_istype"));
            }
        
            for (int i = 0; i < self_len; i++) {
                if (!f(*self_data++)) {
                    return mp_const_false;
                }
            }
        } else {
            switch (type) {
                case IS_UPPER: f = &unichar_isupper; break;
                case IS_LOWER: f = &unichar_islower; break;
                default:
                    nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "unknown type provided for str_uni_istype"));
            }
            
            bool contains_alpha = false;
            
            for (int i = 0; i < self_len; i++) { // only check alphanumeric characters
                if (unichar_isalpha(*self_data++)) {
                    contains_alpha = true;
                    if (!f(*(self_data-1))) {
                        return mp_const_false; // we already incremented
                    }
                }
            }
            
            if (!contains_alpha) {
                return mp_const_false;
            }
        }
    
        return mp_const_true;
    }
    
    STATIC mp_obj_t str_isspace(mp_obj_t self_in) {
        return str_uni_istype(IS_SPACE, self_in);
    }
    
    STATIC mp_obj_t str_isalpha(mp_obj_t self_in) {
        return str_uni_istype(IS_ALPHA, self_in);
    }
    
    STATIC mp_obj_t str_isdigit(mp_obj_t self_in) {
        return str_uni_istype(IS_DIGIT, self_in);
    }
    
    STATIC mp_obj_t str_isupper(mp_obj_t self_in) {
        return str_uni_istype(IS_UPPER, self_in);
    }
    
    STATIC mp_obj_t str_islower(mp_obj_t self_in) {
        return str_uni_istype(IS_LOWER, self_in);
    }
    
    #if MICROPY_CPYTHON_COMPAT
    // These methods are superfluous in the presense of str() and bytes()
    // constructors.
    // TODO: should accept kwargs too
    STATIC mp_obj_t bytes_decode(uint n_args, const mp_obj_t *args) {
        mp_obj_t new_args[2];
        if (n_args == 1) {
            new_args[0] = args[0];
            new_args[1] = MP_OBJ_NEW_QSTR(MP_QSTR_utf_hyphen_8);
            args = new_args;
            n_args++;
        }
        return str_make_new(NULL, n_args, 0, args);
    }
    
    // TODO: should accept kwargs too
    STATIC mp_obj_t str_encode(uint n_args, const mp_obj_t *args) {
        mp_obj_t new_args[2];
        if (n_args == 1) {
            new_args[0] = args[0];
            new_args[1] = MP_OBJ_NEW_QSTR(MP_QSTR_utf_hyphen_8);
            args = new_args;
            n_args++;
        }
        return bytes_make_new(NULL, n_args, 0, args);
    }
    #endif
    
    STATIC machine_int_t str_get_buffer(mp_obj_t self_in, mp_buffer_info_t *bufinfo, int flags) {
        if (flags == MP_BUFFER_READ) {
            GET_STR_DATA_LEN(self_in, str_data, str_len);
            bufinfo->buf = (void*)str_data;
            bufinfo->len = str_len;
            bufinfo->typecode = 'b';
            return 0;
        } else {
            // can't write to a string
            bufinfo->buf = NULL;
            bufinfo->len = 0;
            bufinfo->typecode = -1;
            return 1;
        }
    }
    
    #if MICROPY_CPYTHON_COMPAT
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(bytes_decode_obj, 1, 3, bytes_decode);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_encode_obj, 1, 3, str_encode);
    #endif
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_find_obj, 2, 4, str_find);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_rfind_obj, 2, 4, str_rfind);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_index_obj, 2, 4, str_index);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_rindex_obj, 2, 4, str_rindex);
    STATIC MP_DEFINE_CONST_FUN_OBJ_2(str_join_obj, str_join);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_split_obj, 1, 3, str_split);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_rsplit_obj, 1, 3, str_rsplit);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_startswith_obj, 2, 3, str_startswith);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_endswith_obj, 2, 3, str_endswith);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_strip_obj, 1, 2, str_strip);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_lstrip_obj, 1, 2, str_lstrip);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_rstrip_obj, 1, 2, str_rstrip);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR(str_format_obj, 1, mp_obj_str_format);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_replace_obj, 3, 4, str_replace);
    STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(str_count_obj, 2, 4, str_count);
    STATIC MP_DEFINE_CONST_FUN_OBJ_2(str_partition_obj, str_partition);
    STATIC MP_DEFINE_CONST_FUN_OBJ_2(str_rpartition_obj, str_rpartition);
    STATIC MP_DEFINE_CONST_FUN_OBJ_1(str_lower_obj, str_lower);
    STATIC MP_DEFINE_CONST_FUN_OBJ_1(str_upper_obj, str_upper);
    STATIC MP_DEFINE_CONST_FUN_OBJ_1(str_isspace_obj, str_isspace);
    STATIC MP_DEFINE_CONST_FUN_OBJ_1(str_isalpha_obj, str_isalpha);
    STATIC MP_DEFINE_CONST_FUN_OBJ_1(str_isdigit_obj, str_isdigit);
    STATIC MP_DEFINE_CONST_FUN_OBJ_1(str_isupper_obj, str_isupper);
    STATIC MP_DEFINE_CONST_FUN_OBJ_1(str_islower_obj, str_islower);
    
    STATIC const mp_map_elem_t str_locals_dict_table[] = {
    #if MICROPY_CPYTHON_COMPAT
        { MP_OBJ_NEW_QSTR(MP_QSTR_decode), (mp_obj_t)&bytes_decode_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_encode), (mp_obj_t)&str_encode_obj },
    #endif
        { MP_OBJ_NEW_QSTR(MP_QSTR_find), (mp_obj_t)&str_find_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_rfind), (mp_obj_t)&str_rfind_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_index), (mp_obj_t)&str_index_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_rindex), (mp_obj_t)&str_rindex_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_join), (mp_obj_t)&str_join_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_split), (mp_obj_t)&str_split_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_rsplit), (mp_obj_t)&str_rsplit_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_startswith), (mp_obj_t)&str_startswith_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_endswith), (mp_obj_t)&str_endswith_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_strip), (mp_obj_t)&str_strip_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_lstrip), (mp_obj_t)&str_lstrip_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_rstrip), (mp_obj_t)&str_rstrip_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_format), (mp_obj_t)&str_format_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_replace), (mp_obj_t)&str_replace_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_count), (mp_obj_t)&str_count_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_partition), (mp_obj_t)&str_partition_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_rpartition), (mp_obj_t)&str_rpartition_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_lower), (mp_obj_t)&str_lower_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_upper), (mp_obj_t)&str_upper_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_isspace), (mp_obj_t)&str_isspace_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_isalpha), (mp_obj_t)&str_isalpha_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_isdigit), (mp_obj_t)&str_isdigit_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_isupper), (mp_obj_t)&str_isupper_obj },
        { MP_OBJ_NEW_QSTR(MP_QSTR_islower), (mp_obj_t)&str_islower_obj },
    };
    
    STATIC MP_DEFINE_CONST_DICT(str_locals_dict, str_locals_dict_table);
    
    const mp_obj_type_t mp_type_str = {
        { &mp_type_type },
        .name = MP_QSTR_str,
        .print = str_print,
        .make_new = str_make_new,
        .binary_op = str_binary_op,
        .subscr = str_subscr,
        .getiter = mp_obj_new_str_iterator,
        .buffer_p = { .get_buffer = str_get_buffer },
        .locals_dict = (mp_obj_t)&str_locals_dict,
    };
    
    // Reuses most of methods from str
    const mp_obj_type_t mp_type_bytes = {
        { &mp_type_type },
        .name = MP_QSTR_bytes,
        .print = str_print,
        .make_new = bytes_make_new,
        .binary_op = str_binary_op,
        .subscr = str_subscr,
        .getiter = mp_obj_new_bytes_iterator,
        .buffer_p = { .get_buffer = str_get_buffer },
        .locals_dict = (mp_obj_t)&str_locals_dict,
    };
    
    // the zero-length bytes
    STATIC const mp_obj_str_t empty_bytes_obj = {{&mp_type_bytes}, 0, 0, NULL};
    const mp_obj_t mp_const_empty_bytes = (mp_obj_t)&empty_bytes_obj;
    
    mp_obj_t mp_obj_str_builder_start(const mp_obj_type_t *type, uint len, byte **data) {
        mp_obj_str_t *o = m_new_obj(mp_obj_str_t);
        o->base.type = type;
        o->len = len;
        o->hash = 0;
        byte *p = m_new(byte, len + 1);
        o->data = p;
        *data = p;
        return o;
    }
    
    mp_obj_t mp_obj_str_builder_end(mp_obj_t o_in) {
        mp_obj_str_t *o = o_in;
        o->hash = qstr_compute_hash(o->data, o->len);
        byte *p = (byte*)o->data;
        p[o->len] = '\0'; // for now we add null for compatibility with C ASCIIZ strings
        return o;
    }
    
    mp_obj_t mp_obj_new_str_of_type(const mp_obj_type_t *type, const byte* data, uint len) {
        mp_obj_str_t *o = m_new_obj(mp_obj_str_t);
        o->base.type = type;
        o->len = len;
        if (data) {
            o->hash = qstr_compute_hash(data, len);
            byte *p = m_new(byte, len + 1);
            o->data = p;
            memcpy(p, data, len * sizeof(byte));
            p[len] = '\0'; // for now we add null for compatibility with C ASCIIZ strings
        }
        return o;
    }
    
    mp_obj_t mp_obj_new_str(const char* data, uint len, bool make_qstr_if_not_already) {
        if (make_qstr_if_not_already) {
            // use existing, or make a new qstr
            return MP_OBJ_NEW_QSTR(qstr_from_strn(data, len));
        } else {
            qstr q = qstr_find_strn(data, len);
            if (q != MP_QSTR_NULL) {
                // qstr with this data already exists
                return MP_OBJ_NEW_QSTR(q);
            } else {
                // no existing qstr, don't make one
                return mp_obj_new_str_of_type(&mp_type_str, (const byte*)data, len);
            }
        }
    }
    
    mp_obj_t mp_obj_new_bytes(const byte* data, uint len) {
        return mp_obj_new_str_of_type(&mp_type_bytes, data, len);
    }
    
    bool mp_obj_str_equal(mp_obj_t s1, mp_obj_t s2) {
        if (MP_OBJ_IS_QSTR(s1) && MP_OBJ_IS_QSTR(s2)) {
            return s1 == s2;
        } else {
            GET_STR_HASH(s1, h1);
            GET_STR_HASH(s2, h2);
            // If any of hashes is 0, it means it's not valid
            if (h1 != 0 && h2 != 0 && h1 != h2) {
                return false;
            }
            GET_STR_DATA_LEN(s1, d1, l1);
            GET_STR_DATA_LEN(s2, d2, l2);
            if (l1 != l2) {
                return false;
            }
            return memcmp(d1, d2, l1) == 0;
        }
    }
    
    STATIC void bad_implicit_conversion(mp_obj_t self_in) {
        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_TypeError, "Can't convert '%s' object to str implicitly", mp_obj_get_type_str(self_in)));
    }
    
    STATIC void arg_type_mixup() {
        nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError, "Can't mix str and bytes arguments"));
    }
    
    uint mp_obj_str_get_hash(mp_obj_t self_in) {
        // TODO: This has too big overhead for hash accessor
        if (MP_OBJ_IS_STR(self_in) || MP_OBJ_IS_TYPE(self_in, &mp_type_bytes)) {
            GET_STR_HASH(self_in, h);
            return h;
        } else {
            bad_implicit_conversion(self_in);
        }
    }
    
    uint mp_obj_str_get_len(mp_obj_t self_in) {
        // TODO This has a double check for the type, one in obj.c and one here
        if (MP_OBJ_IS_STR(self_in) || MP_OBJ_IS_TYPE(self_in, &mp_type_bytes)) {
            GET_STR_LEN(self_in, l);
            return l;
        } else {
            bad_implicit_conversion(self_in);
        }
    }
    
    // use this if you will anyway convert the string to a qstr
    // will be more efficient for the case where it's already a qstr
    qstr mp_obj_str_get_qstr(mp_obj_t self_in) {
        if (MP_OBJ_IS_QSTR(self_in)) {
            return MP_OBJ_QSTR_VALUE(self_in);
        } else if (MP_OBJ_IS_TYPE(self_in, &mp_type_str)) {
            mp_obj_str_t *self = self_in;
            return qstr_from_strn((char*)self->data, self->len);
        } else {
            bad_implicit_conversion(self_in);
        }
    }
    
    // only use this function if you need the str data to be zero terminated
    // at the moment all strings are zero terminated to help with C ASCIIZ compatibility
    const char *mp_obj_str_get_str(mp_obj_t self_in) {
        if (MP_OBJ_IS_STR(self_in)) {
            GET_STR_DATA_LEN(self_in, s, l);
            (void)l; // len unused
            return (const char*)s;
        } else {
            bad_implicit_conversion(self_in);
        }
    }
    
    const char *mp_obj_str_get_data(mp_obj_t self_in, uint *len) {
        if (is_str_or_bytes(self_in)) {
            GET_STR_DATA_LEN(self_in, s, l);
            *len = l;
            return (const char*)s;
        } else {
            bad_implicit_conversion(self_in);
        }
    }
    
    /******************************************************************************/
    /* str iterator                                                               */
    
    typedef struct _mp_obj_str_it_t {
        mp_obj_base_t base;
        mp_obj_t str;
        machine_uint_t cur;
    } mp_obj_str_it_t;
    
    STATIC mp_obj_t str_it_iternext(mp_obj_t self_in) {
        mp_obj_str_it_t *self = self_in;
        GET_STR_DATA_LEN(self->str, str, len);
        if (self->cur < len) {
            mp_obj_t o_out = mp_obj_new_str((const char*)str + self->cur, 1, true);
            self->cur += 1;
            return o_out;
        } else {
            return MP_OBJ_STOP_ITERATION;
        }
    }
    
    STATIC const mp_obj_type_t mp_type_str_it = {
        { &mp_type_type },
        .name = MP_QSTR_iterator,
        .getiter = mp_identity,
        .iternext = str_it_iternext,
    };
    
    STATIC mp_obj_t bytes_it_iternext(mp_obj_t self_in) {
        mp_obj_str_it_t *self = self_in;
        GET_STR_DATA_LEN(self->str, str, len);
        if (self->cur < len) {
            mp_obj_t o_out = MP_OBJ_NEW_SMALL_INT((mp_small_int_t)str[self->cur]);
            self->cur += 1;
            return o_out;
        } else {
            return MP_OBJ_STOP_ITERATION;
        }
    }
    
    STATIC const mp_obj_type_t mp_type_bytes_it = {
        { &mp_type_type },
        .name = MP_QSTR_iterator,
        .getiter = mp_identity,
        .iternext = bytes_it_iternext,
    };
    
    mp_obj_t mp_obj_new_str_iterator(mp_obj_t str) {
        mp_obj_str_it_t *o = m_new_obj(mp_obj_str_it_t);
        o->base.type = &mp_type_str_it;
        o->str = str;
        o->cur = 0;
        return o;
    }
    
    mp_obj_t mp_obj_new_bytes_iterator(mp_obj_t str) {
        mp_obj_str_it_t *o = m_new_obj(mp_obj_str_it_t);
        o->base.type = &mp_type_bytes_it;
        o->str = str;
        o->cur = 0;
        return o;
    }