inspect.isfunction doesn't work for all modules?

Question

I'm attempting to use the answer to Is it possible to list all functions in a module? to list functions in a range of modules. But in my interpreter I get as follows:

Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (In
tel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import inspect
>>> import math
>>> math.pow(5,4)
625.0
>>> inspect.getmembers(math, inspect.isfunction)
[]
>>> inspect.getmembers(inspect, inspect.isfunction)
[('_check_class', <function _check_class at 0x00C9F9C0>), ('_check_instance', <f
unction _check_instance at 0x00C9F978>), ('_get_user_defined_method', <function
_get_user_defined_method at 0x00C9FB70>), ('_getfullargs', <function _getfullarg
s at 0x00C6A4F8>), ('_is_type', <function _is_type at 0x00C9FA08>), ('_missing_a
rguments', <function _missing_arguments at 0x00C9F198>), ('_shadowed_dict', <fun
ction _shadowed_dict at 0x00C9FA50>)... foo, bar, etc]

>>> math
<module 'math' (built-in)>
>>> inspect
<module 'inspect' from 'E:\\Python33\\lib\\inspect.py'>

>>> import win32api
>>> inspect.getmembers(win32api, inspect.isfunction)
[]
>>> win32api
<module 'win32api' from 'E:\\Python33\\lib\\site-packages\\win32\\win32api.pyd'>

As per usual, I assume there's some blindingly obvious reason as to why this is failing to list all functions in half the modules I try. The best I can guess is isfunction() only works for .py modules? If there is an innate problem not related to my stupidity, is there a way to rectify this matter?

It's clearly an issue with the isfunction(), as getmembers seems to work fine:

>>> import math
>>> import inspect
>>> inspect.getmembers(math)
[('__doc__', 'This module is always available.  It provides access to the\nmathe
matical functions defined by the C standard.'), ('__loader__', <class '_frozen_i
mportlib.BuiltinImporter'>), ('__name__', 'math'), ('__package__', ''), ('acos',
 <built-in function acos>), ('acosh', <built-in function acosh>), ('asin', <buil
t-in function asin>)... foo, bar, etc]

I understand there's a dir() which can be used, but it's not really quite as neat.

Answer 1

C-defined functions are not instances of the user-defined function type; they are defined in C instead, for which you could use inspect.isbuiltin().

The fool-proof method to list all functions in modules is to use inspect.isroutine() instead:

Return true if the object is a user-defined or built-in function or method.

Demo on the math module:

>>> import inspect
>>> import math
>>> inspect.getmembers(math, inspect.isroutine)
[('acos', <built-in function acos>), ('acosh', <built-in function acosh>), ('asin', <built-in function asin>), ('asinh', <built-in function asinh>), ('atan', <built-in function atan>), ('atan2', <built-in function atan2>), ('atanh', <built-in function atanh>), ('ceil', <built-in function ceil>), ('copysign', <built-in function copysign>), ('cos', <built-in function cos>), ('cosh', <built-in function cosh>), ('degrees', <built-in function degrees>), ('erf', <built-in function erf>), ('erfc', <built-in function erfc>), ('exp', <built-in function exp>), ('expm1', <built-in function expm1>), ('fabs', <built-in function fabs>), ('factorial', <built-in function factorial>), ('floor', <built-in function floor>), ('fmod', <built-in function fmod>), ('frexp', <built-in function frexp>), ('fsum', <built-in function fsum>), ('gamma', <built-in function gamma>), ('hypot', <built-in function hypot>), ('isinf', <built-in function isinf>), ('isnan', <built-in function isnan>), ('ldexp', <built-in function ldexp>), ('lgamma', <built-in function lgamma>), ('log', <built-in function log>), ('log10', <built-in function log10>), ('log1p', <built-in function log1p>), ('modf', <built-in function modf>), ('pow', <built-in function pow>), ('radians', <built-in function radians>), ('sin', <built-in function sin>), ('sinh', <built-in function sinh>), ('sqrt', <built-in function sqrt>), ('tan', <built-in function tan>), ('tanh', <built-in function tanh>), ('trunc', <built-in function trunc>)]

Note the built-in part of the string representation of each function object.

isroutine() returns true if one of inspect.isbuiltin(), inspect.isfunction(), inspect.ismethod() or inspect.ismethoddescriptor() returns True.

Answer 2

Did you read the documentation for isfunction (emphasis added):

Return true if the object is a Python function

So no, it doesn't work for builtin functions.

You could use inspect.isroutine for your test instead. This will still miss objects that define __call__, which may or may not be what you want. You could also use callable for your test, which also may or may not be what you want. It's not always a simple task to know what kind of objects you want to consider "functions", since there may be objects that are meant to act like functions but are not actually functions.