02 April 2005 8 comments Python
Python gurus are going to laugh at me for this one but I learnt it today; how to check if an object is callable. Before this I thought I was clever with this:
>>> def foo(): return "s"
>>> hasattr(foo, '__call__')
True
>>> hasattr(foo(), '__call__')
False
But there was an easier way. I discovered this by accident and looked it up in the documentation after. Use the builtin function called 'callable()':
>>> def foo(): return "s"
>>> callable(foo)
True
>>> callable(foo())
False
D'oh!
According to PEP 3000 the callable built-in function is going to be gone in Python 3.0. In the interest of staying compatible you may want to stick with the old way or call it and catch the exception as the previous comment mentioned. (PEP 3000 - http://www.python.org/peps/pep-3000.html)
Often it pays not to get fancy...
probably the best way (if you can afford to wait until the last possible moment) is to try making the call and catch the TypeError exception
I prefer not to use try and except statements. They look too wild and don't give any performance improvement.
Except for callables which might trigger nuclear weapons.
Good discovery. It helped you.
I tried callable(iter) and callable(candygram.link)
both returned true.....ya I was lazy to write a callable.
"the callable built-in function is going to be gone in Python 3.0"
in that case, hasattr(foo, '__call__') seems more logical (to a second hand reader) than catching the exception, in my opinion..
Python 3.3 shell log:
>>> def Foo():
return Foo
>>> f = Foo()
>>> f
<function Foo at 0x01F45930>
>>> callable(Foo)
True
>>> callable(Foo())
True
>>> callable(f)
True
Is that not what you expect?