Function Object - in Python

In Python

In Python, functions are first-class objects, just like strings, numbers, lists etc. This feature eliminates the need to write a function object in many cases. Any object with a __call__ method can be called using function-call syntax.

An example is this accumulator class (based on Paul Graham's study on programming language syntax and clarity):

class Accumulator(object): def __init__(self, n): self.n = n def __call__(self, x): self.n += x return self.n

An example of this in use (using the interactive interpreter):

>>> a = Accumulator(4) >>> a(5) 9 >>> a(2) 11 >>> b = Accumulator(42) >>> b(7) 49

A function object using a closure in Python 3:

def Accumulator(n): def inc(x): nonlocal n n += x return n return inc