Determine if a function is available in a Python module

Question

I am working on some Python socket code that\'s using the socket.fromfd() function.

However, this method is not available on all platforms, so I am writing some fallback

Answer 1

hasattr(obj, 'attributename') is probably a better one. hasattr will try to access the attribute, and if it's not there, it'll return false.

It's possible to have dynamic methods in python, i.e. methods that are created when you try to access them. They would not be in dir(...). However hasattr would check for it.

>>> class C(object):
...   def __init__(self):
...     pass
...   def mymethod1(self):
...     print "In #1"
...   def __getattr__(self, name):
...     if name == 'mymethod2':
...       def func():
...         print "In my super meta #2"
...       return func
...     else:
...       raise AttributeError
... 
>>> c = C()
>>> 'mymethod1' in dir(c)
True
>>> hasattr(c, 'mymethod1')
True
>>> c.mymethod1()
In #1
>>> 'mymethod2' in dir(c)
False
>>> hasattr(c, 'mymethod2')
True
>>> c.mymethod2()
In my super meta #2

Answer 2

Or simply use a try..except block:

try:
  sock = socket.fromfd(...)
except AttributeError:
  sock = socket.socket(...)

Answer 3

hasattr() is the best choice. Go with that. :)

if hasattr(socket, 'fromfd'):
    pass
else:
    pass

EDIT: Actually, according to the docs all hasattr is doing is calling getattr and catching the exception. So if you want to cut out the middle man you should go with marcog's answer.

EDIT: I also just realized this question is actually a duplicate. One of the answers there discusses the merits of the two options you have: catching the exception ("easier to ask for forgiveness than permission") or simply checking before hand ("look before you leap"). Honestly, I am more of the latter, but it seems like the Python community leans towards the former school of thought.