[Python-3000] py3k-struni: proposition to fix ctypes bug, ctypes c_char creates bytes

[Thomas Heller]

Victor Stinner schrieb:
> Hi,
> 
> I hear Guido's request to fix last py3k-struni bugs. I downloaded subversion 
> trunk and started to work on ctypes tests.
> 
> The problem is that ctypes c_char (and c_char_p) creates unicode string 
> instead of byte string. I attached a proposition (patch) to change this 
> behaviour (use bytes for c_char).
> 
> So in next example, it will display 'bytes' and not 'str':
>   from ctypes import c_buffer, c_char
>   buf = c_buffer("abcdef")
>   print (type(buf[0]))
> 
> Other behaviour changes:
>  - repr(c_char) adds a "b"
>    eg. repr(c_char('x')) is "c_char(b'x')" instead of "c_char('x')"
>  - bytes is mutable whereas str is not: 
>    this may break some modules based on ctypes

This patch looks correct.  I will test it and then commit if all works well.


The problem I had fixing this is that I was not sure whether the c_char types
should 'contain' bytes objects or str8 objects.  str8 will be going away, so
it seems the decision is clear.

OTOH, I'm a little bit confused about the bytes type.  I think this behaviour
is a little bit confusing, but maybe that's just me:

>>> b"abc"[:]
b'abc'
>>> b"abc"[:1]
b'a'
>>> b"abc"[1]
98
>>> b"abc"[1] = 42
>>> b"abc"[1] = "f"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'str' object cannot be interpreted as an integer
>>> b"abc"[1] = b"f"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'bytes' object cannot be interpreted as an integer
>>>

Especially confusing is that the repr of a bytes object looks like a string,
but bytes do not contain characters but integers instead.

Thomas