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Factory-1.2
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Object Oriented Currying
| ویژگی | مقدار |
|---|---|
| سیستم عامل | - |
| نام فایل | Factory-1.2 |
| نام | Factory |
| نسخه کتابخانه | 1.2 |
| نگهدارنده | [] |
| ایمیل نگهدارنده | [] |
| نویسنده | Peter Fein |
| ایمیل نویسنده | pfein@pobox.com |
| آدرس صفحه اصلی | http://code.google.com/p/python-factory/ |
| آدرس اینترنتی | https://pypi.org/project/Factory/ |
| مجوز | UNKNOWN |
Overview
========
Factory is an object-oriented approach to partial function application, also known as currying. The Factory module is a more powerful implementation of this pattern. Some improvements include:
- safer, as invalid arguments are detected immediately, instead of at call time
- intelligent support for classes, instance methods & all other callables
- bound arguments can be inspected and modified as attributes
- several convenient methods for (re)binding arguments
- no "Russian dolls" of nested lambdas
Using Factories can:
- simplify writing callbacks
- reduce bugs in concurrent applications
- provide easy lazy evaluation
Installation
============
The Factory module is available from the `Cheeseshop <http://pypi.python.org/pypi/Factory/>`_. The source code is available from the `Google Code project page <http://code.google.com/p/python-factory/>`_.
The Factory module can be installed like any other pure Python module. Setuptools is supported but not required. You may also include the ``Factory.py`` file directly in your project's source tree, but you must retain the copyright notice and version and attribution information.
To run tests for the module, execute the following commands in the ``Factory/`` directory:
- ``python doctest_Factory.py``
- ``nosetests test_Factory.py``
About Currying
==============
Currying creates a new function from an existing one by binding some of the original's arguments:
>>> def adder(x, y):
... return x + y
>>> add_lambda = lambda y: adder(1, y)
>>> add_lambda(10)
11
As of Python 2.5, this pattern is built in with the `partial <http://docs.python.org/whatsnew/2.5.html#pep-309-partial-function-application>`_ function.
>>> add_partial = functools.partial(adder, 1)
>>> add_partial(y=10)
11
Factories
=========
Factories are better implementation of the currying pattern:
>>> from Factory import *
>>> add_factory = Factory(adder, x=1)
>>> add_factory #doctest: +ELLIPSIS
<Factory(<function adder at ...>) at ...>
>>> add_factory(y=10)
11
Unlike lambdas and partial, factories can be inspected and modified:
>>> add_factory.x
1
>>> add_factory.x = 2
>>> add_factory(y=10)
12
The arguments that would be passed to the function can be examined, which
is sometimes helpful in debugging:
>>> import pprint
>>> args, kwargs = add_factory.generateArgs(y=10)
>>> pprint.pprint(kwargs)
{'x': 2, 'y': 10}
>>> args
[]
Usage
=====
In the following examples, we mix in **FactoryMixin** to provide a
``factory`` classmethod on the base class.
>>> class Foo(FactoryMixin):
... def __init__(self, foo):
... self.foo = foo
...
>>> foo_factory = Foo.factory()
>>> foo_factory.foo = 66
This is equivalent to:
>>> Factory(Foo) #doctest:+ELLIPSIS
<Factory(<class 'Foo'>) at ...>
Using the mixin isn't strictly necessary, but looks nice and is easier to spell.
Factories have a **bind** method that can be used to set several attributes
at once and returns the factory. It's useful for binding arguments
without assigning the factory to a local variable.
>>> def doStuff(foo_factory):
... return foo_factory.foo
>>> doStuff(foo_factory.bind(foo=11))
11
>>> foo_factory2 = foo_factory.bind(foo=42)
>>> foo_factory2 is foo_factory
True
>>> foo_factory.foo
42
You can also bind attributes when constructing the factory:
>>> foo_factory = Factory(Foo, foo=11)
>>> foo_factory.foo
11
Factories ensure that attributes match up with arguments; this makes
finding errors easier (instead of raising a ``unexpected keyword argument``
later):
>>> foo_factory.bar = 42 #doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'No such argument bar'
When calling the factory, arguments override attributes:
>>> foo = foo_factory(foo=1111)
>>> foo.foo
1111
Each call returns a new instance:
>>> foo2 = foo_factory()
>>> foo2 is foo
False
The set of valid attributes is the union of all ``__init__`` arguments in the
inheritance chain:
>>> class Bar(Foo):
... def __init__(self, bar, **kwargs):
... super(Bar, self).__init__(**kwargs)
... self.bar = bar
...
>>> bar_factory = Bar.factory()
>>> bar_factory.foo = 11
>>> bar_factory.bar = 42
>>> bar_factory.quux = 666 #doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'No such argument quux'
>>> bar = bar_factory()
>>> bar.foo
11
>>> bar.bar
42
Be sure to pass Factory a callable object (a class, not an an instance):
>>> Factory(bar) #doctest:+ELLIPSIS, +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: must provide known callable type, not <Factory.Bar object at ...>
Callable objects are fine, of course:
>>> class CallMe(object):
... def __init__(self, x):
... self.x = x
... def __call__(self, y):
... return self.x + y
>>> Factory(CallMe(1))(1)
2
An existing factory can be passed as the ``callee`` of a new factory.
>>> bar_factory = Bar.factory(bar=2)
>>> bar_factory2 = Factory(bar_factory, foo = 1)
>>> bar_factory is not bar_factory2
True
>>> bar_factory2.bar
2
>>> bar_factory2.bar = 4
>>> bar_factory.bar
2
Unlike using lambdas, this does not create nested "Russian dolls":
>>> bar_factory2.getCallable()
<class 'Bar'>
Decorators
==========
**returnFactory** is a decorator which *replaces* a function with its Factory-producing equivalent:
>>> @returnFactory
... def mult(x, y):
... return x * y
>>> fac = mult(x=10, y=5)
>>> isinstance(fac, Factory)
True
>>> fac()
50
**factoryAttribute** adds a ``factory`` attribute to the decorated function:
>>> @factoryAttribute
... def adder(x, y):
... return x + y
>>> fac = adder.factory(x=10)
>>> isinstance(fac, Factory)
True
>>> fac2 = adder.factory()
>>> fac is not fac2
True
>>> fac(y=42)
52
**factoryDescriptor** produces instance methods with a ``factory`` attribute. Inside classes, use this descriptor instead of factoryAttribute. This class may be used as a decorator:
>>> class Quux(object):
... @factoryDescriptor
... def doStuff(self, whatnot):
... pass
>>> quux = Quux()
>>> fac = quux.doStuff.factory(whatnot=42)
>>> isinstance(fac, Factory)
True
>>> fac.whatnot
42
ObjectTemplates
================
ObjectTemplates are a template for creating objects. They work well with Factories.
A **Bunch** is simply a bunch of attributes. Keyword arguments to a Bunch are turned into attributes:
>>> b = Bunch(pants=42, shirt=15)
>>> b.pants
42
>>> b.shirt
15
Calling a bunch returns a new copy:
>>> c = b()
>>> c.__dict__ == b.__dict__
True
>>> c is b
False
When called, an **ObjectTemplate** instance produces a new instance
of ``bunchClass``. Attributes on the template are passed as kwargs
to the bunch. However, if an attribute is callable, it is called
and the return value is used instead:
>>> counter = itertools.count(1).next # an incrementing counter
>>> def color():
... return "blue"
>>> template = ObjectTemplate(size=42,
... color=color,
... count=counter,
... bunchClass=Bunch)
>>> bunch = template()
>>> isinstance(bunch, Bunch)
True
>>> bunch.size
42
>>> bunch.color
'blue'
>>> bunch.count
1
Each call to the template produces a new bunch. Any functions will
be called again:
>>> bunch2 = template()
>>> bunch2.count
2
If you want to pass a callable object to the bunch, wrap it in a lambda:
>>> template = ObjectTemplate()
>>> template.return_val = color
>>> template.a_function = lambda: color
>>> bunch = template()
>>> bunch.return_val
'blue'
>>> bunch.a_function #doctest:+ELLIPSIS
<function color at ...>
Bugs
====
Bugs, feature requests and praise may be sent directly to `the author <mailto:pfein@pobox.com>`_.
نحوه نصب
نصب پکیج whl Factory-1.2:
pip install Factory-1.2.whl
نصب پکیج tar.gz Factory-1.2:
pip install Factory-1.2.tar.gz