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Hacking In Python's Parameter Definition!

Project Description
magic-parameter |Build Status|
==============================

**WARNING: Interfaces of this project is UNSTABLE, might be changed in
the future!**

``magic-parameter`` handles type checking for you.

Install
-------

::

pip install magic-parameter

Supports Python 2.7 and 3.3+.

Usage
-----

Concepts
~~~~~~~~

Parameter Declaration:

- ``(<name>, <type declaration>)``
- ``(<name>, <type declaration>, <default value>)``
- ``(<name>, <type declaration>, None)``

Type Declaration:

- any **type object**, i.e. ``list``, ``int``, ``str``, ``FooBar``.
- instance of ``magic-parameter.<nested type>``:

- ``magic_parameter.list_t(<type declaration>)``
- ``magic_parameter.tuple_t(<type declaration>)``
- ``magic_parameter.set_t(<type declaration>)``
- ``magic_parameter.dict_t(<key type declaration>, <val type declaration>)``

- instance of ``magic-parameter.<relation type>``

- ``magic_parameter.or_t(<type declaration>, ...)``

Decorators:

- ``magic_parameter.function_parameter``
- ``magic_parameter.method_parameter``
- ``magic_parameter.method_init_parameter``
- ``magic_parameter.class_init_parameter``

``function_parameter(raw_parameter_decls)``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``function_parameter`` is a function decorator.

Flowing example defines a function with parameter ``a`` that accepts
``list`` of ``int``\ s.

.. code:: python

from magic_parameter import function_parameter, list_t


@function_parameter([
('a', list_t(int)),
])
def func(args):
return args.a

Runtime:

.. code:: ipython

In [2]: func([1, 2, 3])
Out[2]: [1, 2, 3]
In [3]: func([1, 2.0, 3])
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
...
TypeError: Rule:
name: None
type: <class 'int'>
Arg: 2.0

``method_parameter(raw_parameter_decls, pass_by_function_argument=False, pass_by_cls_or_self_attributes=False, no_warning_on_cls_or_self_attributes=True)``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``method_parameter`` is a class method decorator. ``method_parameter``
provides two ways to pass arguments:

#. By function argument, same as function\_parameter. In this case,
``pass_by_function_argument`` should be set as ``True``.
#. By attributes binding to the first parameter of class method. In this
case, ``pass_by_cls_or_self_attributes`` should be set as ``True``.
By default, ``no_warning_on_cls_or_self_attributes=True``, meaning
there's no warning on attribute override.

Flowing example defines a class with two methods:

#. ``func1`` is a ``classmethod`` with a parameter ``a``, accepting a
``dict`` with ``str`` as its key and ``int`` as its value.
#. ``func2`` is a function with a parameter ``a``, accepting a ``list``
or a ``tuple``.

.. code:: python

from magic_parameter import method_parameter, dict_t, or_t


class Example(object):

@classmethod
@method_parameter(
[
('a', dict_t(str, int)),
],
pass_by_function_argument=True,
)
def func1(cls, args):
return args.a

@method_parameter(
[
('a', or_t(list, tuple)),
],
pass_by_cls_or_self_attributes=True,
)
def func2(self):
return self.a

Runtime:

.. code:: ipython

In [8]: Example.func1({'k1': 1, 'k2': 2})
Out[8]: {'k1': 1, 'k2': 2}
In [9]: Example.func1({'k1': 1, 1: 2})
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
...
TypeError: Rule:
name: None
type: <class 'str'>
Arg: 1

In [16]: example = Example()

In [17]: example.func2([1, 2, 3])
Out[17]: [1, 2, 3]

In [18]: example.func2((1, 2, 3))
Out[18]: (1, 2, 3)

In [19]: example.func2(1)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
...
TypeError: 1 cannot match [<magic_parameter.type_declaration.TypeDecl object at 0x1076ac048>, <magic_parameter.type_declaration.TypeDecl object at 0x1076ac080>]

``method_init_parameter(raw_parameter_decls)``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``method_init_parameter`` could be viewed as ``method_parameter`` with
``pass_by_cls_or_self_attributes=True, no_warning_on_cls_or_self_attributes=True``
partial binding. It's designed to declare the parameters of ``__init__``
class method.

Following example defines a class accepting an ``int`` for the
initialization.

.. code:: python

from magic_parameter import method_init_parameter


class Example(object):

@method_init_parameter([
('a', int),
])
def __init__(self):
print(self.a)

Runtime:

.. code:: ipython

In [3]: Example(1)
1
Out[3]: <__main__.Example at 0x1029bda20>

In [4]: Example(1.0)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
...
TypeError: Rule:
name: None
type: <class 'int'>
Arg: 1.0

``class_init_parameter(user_defined_class)``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``class_init_parameter`` is a class decorator. ``class_init_parameter``
will extract parameter declarations from
``user_defined_class.PARAMETERS``, then inject a ``__init__`` function
to ``user_defined_class``.

Following example defines a class accepting an ``int`` for the
initialization.

.. code:: python

from magic_parameter import class_init_parameter


@class_init_parameter
class Example1(object):

PARAMETERS = [
('a', int),
]


@class_init_parameter
class Example2(object):

PARAMETERS = [
('a', int),
]

def __init__(self):
print(self.a)

Runtime:

.. code:: ipython

In [5]: Example1(1)
Out[5]: <f.Example1 at 0x106b529b0>

In [6]: Example1(a=1)
Out[6]: <f.Example1 at 0x106ba83c8>

In [7]: Example1(1.0)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
...
TypeError: Rule:
name: None
type: <class 'int'>
Arg: 1.0

In [8]: Example2(1)
1
Out[8]: <f.Example2 at 0x107405828>

.. |Build Status| image:: https://travis-ci.org/huntzhan/magic-parameter.svg?branch=master
:target: https://travis-ci.org/huntzhan/magic-parameter
Release History

Release History

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0.1.0

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0.1.0rc1

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0.1.0.dev0

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