Python function overloading

by

What you are asking for is called multiple dispatch. See Julia language examples which demonstrates different types of dispatches.

However, before looking at that, we’ll first tackle why overloading is not really what you want in Python.

Why Not Overloading?

First, one needs to understand the concept of overloading and why it’s not applicable to Python.

When working with languages that can discriminate data types at
compile-time, selecting among the alternatives can occur at
compile-time. The act of creating such alternative functions for
compile-time selection is usually referred to as overloading a
function. (Wikipedia)

Python is a dynamically typed language, so the concept of overloading simply does not apply to it. However, all is not lost, since we can create such alternative functions at run-time:

In programming languages that defer data type identification until
run-time the selection among alternative
functions must occur at run-time, based on the dynamically determined
types of function arguments. Functions whose alternative
implementations are selected in this manner are referred to most
generally as multimethods. (Wikipedia)

So we should be able to do multimethods in Python—or, as it is alternatively called: multiple dispatch.

Multiple dispatch

The multimethods are also called multiple dispatch:

Multiple dispatch or multimethods is the feature of some
object-oriented programming languages in which a function or method
can be dynamically dispatched based on the run time (dynamic) type of
more than one of its arguments. (Wikipedia)

Python does not support this out of the box1, but, as it happens, there is an excellent Python package called multipledispatch that does exactly that.

Solution

Here is how we might use multipledispatch2 package to implement your methods:

>>> from multipledispatch import dispatch
>>> from collections import namedtuple
>>> from types import *  # we can test for lambda type, e.g.:
>>> type(lambda a: 1) == LambdaType
True

>>> Sprite = namedtuple('Sprite', ['name'])
>>> Point = namedtuple('Point', ['x', 'y'])
>>> Curve = namedtuple('Curve', ['x', 'y', 'z'])
>>> Vector = namedtuple('Vector', ['x','y','z'])

>>> @dispatch(Sprite, Point, Vector, int)
... def add_bullet(sprite, start, direction, speed):
...     print("Called Version 1")
...
>>> @dispatch(Sprite, Point, Point, int, float)
... def add_bullet(sprite, start, headto, speed, acceleration):
...     print("Called version 2")
...
>>> @dispatch(Sprite, LambdaType)
... def add_bullet(sprite, script):
...     print("Called version 3")
...
>>> @dispatch(Sprite, Curve, int)
... def add_bullet(sprite, curve, speed):
...     print("Called version 4")
...

>>> sprite = Sprite('Turtle')
>>> start = Point(1,2)
>>> direction = Vector(1,1,1)
>>> speed = 100 #km/h
>>> acceleration = 5.0 #m/s**2
>>> script = lambda sprite: sprite.x * 2
>>> curve = Curve(3, 1, 4)
>>> headto = Point(100, 100) # somewhere far away

>>> add_bullet(sprite, start, direction, speed)
Called Version 1

>>> add_bullet(sprite, start, headto, speed, acceleration)
Called version 2

>>> add_bullet(sprite, script)
Called version 3

>>> add_bullet(sprite, curve, speed)
Called version 4

1. Python 3 currently supports single dispatch
2. Take care not to use multipledispatch in a multi-threaded environment or you will get weird behavior.

More Related Contents:

  1. Understanding Python super() with __init__() methods [duplicate]
  2. What is the purpose of the word ‘self’?
  3. What is the difference between old style and new style classes in Python?
  4. How do I call a parent class’s method from a child class in Python?
  5. difference between variables inside and outside of __init__()
  6. Explaining the ‘self’ variable to a beginner [duplicate]
  7. How do I use method overloading in Python?
  8. What is the purpose of the `self` parameter for methods?
  9. What is the `self` parameter in class methods?
  10. Attaching a decorator to all functions within a class
  11. How do I access Class member variables in Python?
  12. List all base classes in a hierarchy of given class?
  13. Does Python have class prototypes (or forward declarations)?
  14. How to properly overload the __add__ method?
  15. What is the purpose of python’s inner classes?
  16. Prevent creating new attributes outside __init__
  17. The scope of names defined in class block doesn’t extend to the methods’ blocks. Why is that?
  18. How to implement a binary search tree in Python?
  19. Python: how to “kill” a class instance/object?
  20. What is the purpose of the `self` parameter? Why is it needed?
  21. difference between variables inside and outside of __init__() (class and instance attributes)
  22. How do I access instance variables in Python?
  23. How do I access Class member variables?
  24. How do I set and access attributes of a class? [duplicate]
  25. How to assign a new class attribute via __dict__?
  26. What are the consequences of nesting classes? [closed]
  27. How do you change the value of one attribute by changing the value of another? (dependent attributes)
  28. Correctly extend a tkinter widget using inheritance
  29. Should I use a class or dictionary?
  30. Type Hinting for objects of type that’s being defined [duplicate]

Leave a Comment