How to determine if the variable is a function in Python? [duplicate]

Question

Since functions are values in Python, how do I determine if the variable is a function?

For example:

boda = len   # boda is the length function now
if ?is_var_function(boda)?:
  print "Boda is a function!"
else:
  print "Boda is not a function!"

Here hypothetical ?is_var_function(x)? should return true if x is a callable function, and false if it is not.

Answer 1

You may use inspect.isfunction(object). See: docs.python.org

That said, you should avoid using this technique in your day-to-day code. Sometimes you actually need to use reflection - for example, an MVC framework might need to load a class and inspect its members. But usually you should return/pass/deal with objects that have the same "interface". For example, do not return an object that may be an integer or a function - always return the same "type" of object so your code can be consistent.

Answer 2

The callable built-in mentioned in other answers doesn't answer your question as posed, because it also returns True, besides functions, for methods, classes, instances of classes which define a __call__ method. If your question's title and text are wrong, and you don't care if something is in fact a function but only if it's callable, then use that builtin. But the best answer to your question as posed is: import the inspect method of Python's standard library, and use inspect.isfunction. (There are other, lower-abstraction ways, but it's always a good idea to use functionality of the inspect module for introspection when it's there, in preference to lower-level approaches: inspect helps keep your code concise, clear, robust, and future-proof).