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Project description
Delegate methods made easy
This tiny library implements two simple ways of method delegators.
From wikipedia, what is delegation
In object-oriented programming, delegation refers to evaluating a member (property or method) of one object (the receiver) in the context of another original object (the sender). Delegation can be done explicitly, by passing the sending object to the receiving object, which can be done in any object-oriented language; or implicitly, by the member lookup rules of the language, which requires language support for the feature.
So if you're using compostion, I mean, one object made othe other objects, soon or latter you will want to delegate method calls from composed objects to component ones.
Installation
This is python3 only, but it's very simple library with no dependences, it would not be hard to port it to python2, contributions are welcome!
pip install delegateto
Examples extracted from Doctest
DelegateTo descriptor let you delegate method calls
The argument name is the name of the method that you want to delegate, for example.
from delegateto import DelegateTo
class Foo:
upper = DelegateTo('v')
__len__ = DelegateTo('l')
__iter__ = DelegateTo('l')
def __init__(self, v, l):
self.v = v
self.l = l
foo = Foo('hello world', [1, 2, 3])
To call a method just call its delegator
foo.upper() # => 'HELLO WORLD'
Magic methods are supported
len(foo) # => 3
[x*2 for x in foo] # => [2, 4, 6]
At class parsing time is not possible for DelegateTo
to know to what
attribute you're assign it to. For example foo = DelegateTo('bar')
Pay
attention that DelegateTo
doesn't receive anyinformation about foo
attribute, but it will discover this latter. The method name is discovered at
the first call. This is done by iterating over all the object's attributes.
Once found the method is cached and no search is performed in the subsequent
calls.
Still, if you need to avoid this iteration you can initialize the method name with the same name of the attibute name. For example
class Foo:
upper = DelegateTo('v', 'upper')
def __init__(self, v):
self.v = v
This make possible the creation of aliases
class Foo:
up = DelegateTo('v', 'upper')
def __init__(self, v):
self.v = v
Foo('hello').up() # => 'HELLO'
In this context 'self' has a special meaning of delegating a method to another method in the same object. For example
class Foo:
foo = DelegateTo('self', 'bar')
def bar(self):
return 'bar'
Foo().foo() # => 'bar'
There is another way of creating delegators with class decorators, here is how
from delegateto import delegate
@delegate('v', 'upper')
@delegate('v', 'lower')
@delegate('v', 'wrong_method')
@delegate('not_an_attribute', 'wrong_attribute')
class Foo:
def __init__(self, v):
self.v = v
Foo('foo').upper() # => 'FOO'
Foo('FOO').lower() # => 'foo'
Foo('foo').wrong_method() # => raises AttributeError: 'str' object has no attribute 'wrong_method'
Foo('foo').wrong_attribute() # => raises AttributeError: 'Foo' object has no attribute 'not_an_attribute'
As a shortcut you can use pass any number of methods to delegate
@delegate('v', 'upper', 'lower')
class Foo:
def __init__(self, v):
self.v = v
Running tests
Simple run the module python -m delegateto
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