cython - Extra elements in Python list -

using cython, trying convert python list cython array, , vice versa. python list contains numbers range 0 - 255, specify type of array unsigned char array. here code conversions:

from libc.stdlib cimport malloc  cdef to_array(list pylist):     cdef unsigned char *array      array = <unsigned char *>malloc(len(pylist) * sizeof(unsigned char))     cdef long count = 0      item in pylist:         array[count] = item         count += 1     return array  cdef to_list(array):     pylist = [item item in array]     return pylist  def donothing(pylist):     return to_list(to_array(pylist)) 

the problem lies in fact pieces of garbage data generated in cython array, , when converted python lists, garbage data carries over. example, donothing should absolutely nothing, , return python list me, unchanged. function testing conversion, when run like:

in[56]:  donothing([2,3,4,5]) out[56]: [2, 3, 4, 5, 128, 28, 184, 6, 161, 148, 185, 69, 106, 101] 

where data coming in code, , how can garbage cleaned no memory wasted?

p.s. there may better version of taking numbers python list , injecting them unsigned char array. if so, please direct me better method entirely.

your to_array has untyped return value. further, assign result untyped value. such, cython forced convert char * python type.

cython converts bytes, because char approximately bytes. unfortunately, without explicitly-given length cython assumes char * null-terminated. causes problem:

convert_lists.donothing([1, 2, 3, 0, 4, 5, 6]) #>>> [1, 2, 3] 

when there no zeroes, cython read until finds one, going past actually-allocated memory.

you can't for x in my_pointer_arrray arbitrary cython types. for loop operates on incorrectly-converted bytes.

you can fix typing all values hold char array, passing around length explicitly , looping on ranges (which faster when loop variable typed), or using wrapper of sort. ideas on wrapper arrays use, this question , answer pair has covered.

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please note should very careful errors when using manual allocation. malloc'd data not garbage collected, if error out of code-path you're going leak memory. should check how handle each specific case.