Missing attribute `value` for equal ctypes array objects

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!

Answer

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.