[issue12142] Reference cycle when importing ctypes

[Vlad Riscutia]

Vlad Riscutia <riscutiavlad at gmail.com> added the comment:

I ran full test suit after making the _array_type = type(Array) change and everything passes.

I also took a look at this and found additional leak. gc shows this as garbage:

[(<class '_ctypes._SimpleCData'>,), <class 'ctypes.c_longdouble'>, <attribute '_
_dict__' of 'c_longdouble' objects>, <attribute '__weakref__' of 'c_longdouble'
objects>, (<class 'ctypes.c_longdouble'>, <class '_ctypes._SimpleCData'>, <class
 '_ctypes._CData'>, <class 'object'>), {'__dict__': <attribute '__dict__' of 'c_
longdouble' objects>, '_type_': 'g', '__module__': 'ctypes', '__weakref__': <att
ribute '__weakref__' of 'c_longdouble' objects>, '__doc__': None}]

This is all caused by these lines in ctypes __init__.py:

class c_longdouble(_SimpleCData):
    _type_ = "g"
if sizeof(c_longdouble) == sizeof(c_double):
    c_longdouble = c_double

For me sizeof(c_longdouble) == sizeof(c_double) (I believe MS compiler always does this) but when we assign c_longdouble = c_double, there is a leak. I removed the alias lines:

if sizeof(c_longdouble) == sizeof(c_double):
    c_longdouble = c_double

And the leak was gone. Looks like changing c_longdouble after declaring it causes a leak. Below for similar aliasing of longlong types, we have this:

if _calcsize("l") == _calcsize("q"):
    # if long and long long have the same size, make c_longlong an alias for c_long
    c_longlong = c_long
    c_ulonglong = c_ulong
else:
    class c_longlong(_SimpleCData):
        _type_ = "q"
    _check_size(c_longlong)

    class c_ulonglong(_SimpleCData):
        _type_ = "Q"

This avoids declaring c_longlong and c_ulonglong as class if not needed to. The problem is _calcsize("g") causes an error because "g" is used as long double througout ctypes but _calcsize is function from _struct.c, where "g" (long double) is not defined. Not sure why it isn't...

So in short:
As far as I can tell _array_type = type(Array) doesn't break anything
Looks like we have another leak in ctypes (which isn't a big deal)
We have elegant fix for the leak once _struct.c will support long double

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nosy: +vladris

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue12142>
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