I know 2 ways of creating a c array out of a python sequence data = (1, 2, 3, 4, 5, 6)
.
Creating an array class, initializing it and passing the values through the value
attribute:
array_type = ctypes.c_int * len(data)
array1 = array_type()
array1.value = data
Creating an array class and passing the value as arguments during initialization:
array_type = ctypes.c_int * len(data)
array2 = array_type(*data)
# Or 'array2 = (ctypes.c_int * len(data))(*data)'
Both generates the same type:
>>> array1
<c_int_Array_6 object at 0x1031d9510>
>>> array2
<c_int_Array_6 object at 0x1031d9400>
But when trying to access the value attribute:
array1.value
>>> (1, 2, 3, 4, 5, 6, 7, 8, 9)
array2.value
>>> AttributeError: 'c_int_Array_6' object has no attribute 'value'
Why doesn't array2
has a value
attribute? My understanding is that these arrays are the same type but just initialized differently.
And even if I create two different arrays with two different values, the problem still occurs:
char_array = (c_char * 4)(*data)
print(char_array.value) # Works!
int_array = (c_int * 4)(*data)
print(int_array.value) # Doesn't work!
You define array1.value
as data
. But you didn't specifically define array2.value
. By default .value
is not define (even if the array contains the values).
>>> import ctypes
>>> # Same commands that you provide
>>> # ...
>>> array1.value
(1, 2, 3, 4, 5, 6)
>>> array2.value
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'c_int_Array_6' object has no attribute 'value'
>>> list(array2)
[1, 2, 3, 4, 5, 6]
>>> array2[0]
1
>>> data_bis = (1,4,5)
>>> array2.value = data_bis
>>> array2
<__main__.c_int_Array_6 object at 0x7f86dc981560>
>>> array2.value
(1, 4, 5)
As you can see, you can still have access to the values of array2
using standard python call for list.
You can have a look at Python's documentation, especially on fundamental data types and on arrays and pointers.