ctypes load a dll without error message, but nothing happened

Question

I tried to use windll.LoadLibrary in ctypes to import a dll file into python. Though there wasn\'t any error message, none of the functions listed in the header file seemed to b

Answer 1

They don't show up when you use dir unless you've already accessed the function. For example:

In [98]: from ctypes import cdll

In [99]: libc = cdll.LoadLibrary('libc.so.6')

In [100]: dir(libc)
Out[100]:
['_FuncPtr',
 '__class__',
 '__delattr__',
 '__dict__',
 '__doc__',
 '__format__',
 '__getattr__',
 '__getattribute__',
 '__getitem__',
 '__hash__',
 '__init__',
 '__module__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 '__weakref__',
 '_func_flags_',
 '_func_restype_',
 '_handle',
 '_name']

In [101]: libc.printf
Out[101]: <_FuncPtr object at 0x65a12c0>

In [102]: dir(libc)
Out[102]:
['_FuncPtr',
 '__class__',
 '__delattr__',
 '__dict__',
 '__doc__',
 '__format__',
 '__getattr__',
 '__getattribute__',
 '__getitem__',
 '__hash__',
 '__init__',
 '__module__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 '__weakref__',
 '_func_flags_',
 '_func_restype_',
 '_handle',
 '_name',
 'printf']

You can see why this happens by looking at the CDLL.__getitem__ and CDLL.__getattr__ methods:

class CDLL(object):
    # ...

    def __getattr__(self, name):
        if name.startswith('__') and name.endswith('__'):
            raise AttributeError(name)
        func = self.__getitem__(name)
        setattr(self, name, func)
        return func

    def __getitem__(self, name_or_ordinal):
        func = self._FuncPtr((name_or_ordinal, self))
        if not isinstance(name_or_ordinal, (int, long)):
            func.__name__ = name_or_ordinal
        return func