do mixin for python

This project wants to implement a mixin library like ruby's module.

What mixin is

In object-oriented programming languages, a mixin is a class which contains a combination of methods from other classes. How such a combination is done depends on the language, but it is not by inheritance. If a combination contains all methods of combined classes it is equivalent to multiple inheritance. For more information, please refer to this wiki: http://en.wikipedia.org/wiki/Mixin

install pymixin

install it from pip:

pip install mixin

In fact, the pymix package only has one file, it is mixin.py, so you can also copy it directly to your project directory.

how to use pymixin

a simple example

Import the Mixin class and mixin decorator from the mixin module:

>>> from mixin import Mixin, mixin

The user's mixin class should always inherit from the Mixin class:

>>> class MixinA(Mixin):
...     def func_mixin_a(self):
...             return 'do_func_mixin_a'
...

and then use the mixin decorator to add the mixin to a class:

>>> @mixin(MixinA)
... class A(object): pass
...
>>> a = A()
>>> a.func_mixin_a()
'do_func_mixin_a'

add a mixin to another mixin

The mixin should not be inherited by another class:

>>> class MixinA(Mixin): pass
...
>>> class A(MixinA): pass
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "mixin.py", line 58, in __new__
    raise InheritMixinError(clsname)
__main__.InheritMixinError: A

But you can add a mixin to another mixin:

>>> class MixinA(Mixin):
...     def func_mixin_a(self):
...             return 'do_func_mixin_a'
...
>>> @mixin(MixinA)
... class MixinB(Mixin):
...     def func_mixin_b(self):
...             return 'do_func_mixin_b'
...

Then add the MixinB to a normal class

>>> @mixin(MixinB)
... class M(object): pass
...
>>> m = M()
>>> m.func_mixin_a()
'do_func_mixin_a'
>>> m.func_mixin_b()
'do_func_mixin_b'

a mixin class can not be instantiated

>>> class MixinA(Mixin): pass
...
>>> a = MixinA()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "mixin.py", line 44, in mixin_new
    raise InstantiationMixinError(cls)
__main__.InstantiationMixinError: <class '__main__.MixinA'>

inherit multi mixin

Two kind of methods to inherit multi mixins, one is writing multi mixins in one decorator:

>>> class MixinA(Mixin): pass
...
>>> class MixinB(Mixin): pass
...
>>> @mixin(MixinA, MixinB)
... class M(object): pass
...

Another is using multi decorators:

>>> @mixin(MixinA)
... @mixin(MixinB)
... class M(object): pass
...

inherit priority

When writes multi mixins to one decorator, the left mixin has a higher priority

>>> class MixinA(Mixin):
...     def mixin_func(self):
...             return 'do_mixin_a'
...
>>> class MixinB(Mixin):
...     def mixin_func(self):
...             return 'do_mixin_b'
...
>>> @mixin(MixinA, MixinB)
... class M(object): pass
...
>>> m = M()
>>> m.mixin_func()
'do_mixin_a'

When writes multi mixins in multi decorators, the up mixin has a higher priority:

>>> @mixin(MixinA)
... @mixin(MixinB)
... class M(object): pass
...
>>> m = M()
>>> m.mixin_func()
'do_mixin_a'

If the class has a funciton which has the same name as the mixin, the mixin method will be overwrite:

>>> class MixinA(Mixin):
...     def mixin_func(self):
...             return 'do_mixin_a'
...
>>> @mixin(MixinA)
... class A(object):
...     def mixin_func(self):
...             return 'real_class_mixin_a'
...
>>> a = A()
>>> a.mixin_func()
'real_class_mixin_a'

If a class has a father class, and the father class has a same name method as the mixin, the father class' method will be overwrite:

>>> class MixinA(Mixin):
...     def mixin_func(self):
...             return 'do_mixin_a'
...
>>> class Father(object):
...     def mixin_func(self):
...             return 'father_mixin'
...
>>> @mixin(MixinA)
... class A(Father): pass
...
>>> a=A()
>>> a.mixin_func()
'do_mixin_a'

python version support

Tested on python2.6, python2.7 and python3.4