Fast string array - Cython

Try following code. to_cstring_array function in the following code is what you want.

from libc.stdlib cimport malloc, freefrom libc.string cimport strcmpfrom cpython.string cimport PyString_AsStringcdef char ** to_cstring_array(list_str):    cdef char **ret = <char **>malloc(len(list_str) * sizeof(char *))    for i in xrange(len(list_str)):        ret[i] = PyString_AsString(list_str[i])    return retdef foo(list_str1, list_str2):    cdef unsigned int i, j    cdef char **c_arr1 = to_cstring_array(list_str1)    cdef char **c_arr2 = to_cstring_array(list_str2)    for i in xrange(len(list_str1)):        for j in xrange(len(list_str2)):            if i != j and strcmp(c_arr1[i], c_arr2[j]) == 0:                print i, j, list_str1[i]    free(c_arr1)    free(c_arr2)foo(['hello', 'python', 'world'], ['python', 'rules'])

If you're on Python 3, here's an update to @falsetru's answer (untested on Python 2).

cdef extern from "Python.h":    char* PyUnicode_AsUTF8(object unicode)from libc.stdlib cimport malloc, freefrom libc.string cimport strcmpcdef char ** to_cstring_array(list_str):    cdef char **ret = <char **>malloc(len(list_str) * sizeof(char *))    for i in xrange(len(list_str)):        ret[i] = PyUnicode_AsUTF8(list_str[i])    return retdef foo(list_str1, list_str2):    cdef unsigned int i, j    cdef char **c_arr1 = to_cstring_array(list_str1)    cdef char **c_arr2 = to_cstring_array(list_str2)    for i in range(len(list_str1)):        for j in range(len(list_str2)):            if i != j and strcmp(c_arr1[i], c_arr2[j]) == 0:                print(i, j, list_str1[i])    free(c_arr1)    free(c_arr2)foo(['hello', 'python', 'world'], ['python', 'rules'])

Warning: The pointer returned by PyUnicode_AsUTF8 is cached in the parent unicode-object. Which has two consequences:

1. this pointer is only valid as long as the parent unicode-object is alive. Accessing it afterwards leads to undefined behavior (e.g. possible segmentation fault).
2. The caller of the PyUnicode_AsUTF8 isn't responsible for the freeing the memory.