Having following hypothetical code:
cdef extern from "string.h":
int strcmp(char* str1, char* str2)
def foo(list_str1, list_str2):
cdef unsigned int i, j
c_arr1 = ??
c_arr2 = ??
for i in xrange(len(list_str1)):
for j in xrange(len(list_str2)):
if not strcmp(c_arr1[i], c_arr2[j]):
do some funny stuff
is there some way how to convert the lists to c arrays?
I have read and tried Cython - converting list of strings to char ** but that only throws errors.
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, free
from libc.string cimport strcmp
cdef 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 ret
def 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:
PyUnicode_AsUTF8
isn't responsible for the freeing the memory.Try following code. to_cstring_array
function in the following code is what you want.
from libc.stdlib cimport malloc, free
from libc.string cimport strcmp
from cpython.string cimport PyString_AsString
cdef 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 ret
def 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'])
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