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simple provision of method overloading

Project description

Simple overloading of 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 signature')
TypeError: invalid call signature

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)

  • 1.0 the initial release

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

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