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Simple overloading of methods and functions through an @overload decorator

Project description

Simple overloading of methods and functions through an @overload decorator.

This module allows one to provide multiple interfaces for a functions, methods, classmethods, staticmethods or classes. See below for some notes about overloading classes, you strange person you.

The appropriate implementation is chosen based on the calling argument pattern.

For example:

>>> class A(object):
...   @overload
...   def method(self, a):
...     return 'a'
...   @method.add
...   def method(self, a, b):
...     return 'a, b'
>>> a = A()
>>> a.method(1)
>>> a.method(1, 2)
'a, b'

The overloading handles fixed, keyword, variable (*args) and arbitrary keyword (**keywords) arguments.

It also handles annotations if those annotations are types:

>>> @overload
... def func(a:int):
...   return 'int'
>>> @func.add
... def func(a:str):
...   return 'str'
>>> func(1)
>>> func('s')
>>> func(1.0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "", line 94, in f
    raise TypeError('invalid call argument(s)')
TypeError: invalid call argument(s)

This feature (and currently the module in general) requires Python 3.

The docstring and name (ie. documentation) of the resultant callable will match that of the first callable overloaded.

Overloading Classes

Overloading classes allows you to select a class type based on the construction arguments of each alternative type’s __new__ method.

There’s a catch though: the __new__ method must explicitly invoke the base class __new__ method, rather than use super() like usual. This is because after being @overloaded the class is a function, and super() doesn’t like being passed functions. So instead of:

class A(object):
    def __new__(cls):
        # this will fail because "A" is a function now
        return super(A, cls).__new__(cls)

you must:

class A(object):
    def __new__(cls):
        # must explicitly reference the base class
        return object.__new__(cls)

I’ll leave it up to the reader to justify their use of @overloading classes.

Version History (in Brief)

  • 1.1 altered the text of the invalid call TypeError. Removed debug prints.
  • 1.0 the initial release

See the end of the source file for the license of use.

I would be interested to know whether this module is useful - if you use it please indicate so at

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