[ACCEPTED]-python factory functions compared to class-function

Accepted answer
Score: 29

What I like most about nested functions 11 is that it is less verbose than classes. The 10 equivalent class definition to your maker 9 function is:

class clsmaker(object):
    def __init__(self, N):
        self.N = N
    def __call__(self, X):
        return X * self.N

That doesn't seem so bad until 8 you start adding more arguments to the constructor. Then 7 doing it the class way takes an extra line 6 for each argument, while the function just 5 gets the extra args.

It turns out that there 4 is a speed advantage to the nested functions 3 as well:

>>> T1 = timeit.Timer('maker(3)(4)', 'from __main__ import maker')
>>> T1.timeit()
>>> T2 = timeit.Timer('clsmaker(3)(4)', 'from __main__ import clsmaker')
>>> T2.timeit()

This may be due to there being fewer 2 opcodes involved in the nested functions 1 version:

>>> dis(clsmaker.__call__)
  5           0 LOAD_FAST                1 (X)
              3 LOAD_FAST                0 (self)
              6 LOAD_ATTR                0 (N)
              9 BINARY_MULTIPLY     
             10 RETURN_VALUE        
>>> act = maker(3)
>>> dis(act)
  3           0 LOAD_FAST                0 (X)
              3 LOAD_DEREF               0 (N)
              6 BINARY_MULTIPLY     
              7 RETURN_VALUE  
Score: 18

Comparing a function factory to a class 7 is comparing apples and oranges. Use a 6 class if you have a cohesive collection 5 of data and functions, together called an 4 object. Use a function factory if you need 3 a function, and want to parameterize its 2 creation.

Your choice of the two techniques 1 should depend on the meaning of the code.

Score: 6

Nesting functions allows one to create custom 5 functions on the fly.

Have a look at e.g. decorators. The 4 resulting functions depend on variables 3 that are bound at creation time and do 2 not need to be changed afterwards. So using 1 a class for this purpose would make less sense.

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