Augment 0.2

Python decorators for contracts and augmenting OOP.

Augment
-------

Python decorators for contracts and augmenting OOP.
from distutils.core import setup


Contracts.
``````````

The syntax below should be self explanatory. It can be applied both to bound and unbound methods.

::

# Constraints on passed arguments.
# Constraints can be callables or regular expressions.
# Throws a `TypeError` by default if contraints are violated.
# Optionally, an error handler can be specified which receives the errors.
@ensure_args(a=lambda x: x > 10,
b=r'^?-\d+(\.\d+)$',
c=lambda x: x < 5) # `c` will be picked from `kwargs`.
def foo(a, b, **kwargs):
pass

# Ensure at least one of the constraints is true.
@ensure_one_of(a=lambda x: x, b=lambda x: x)
def foo(a, b):
pass

# Ensures only one of the constraints is true.
@ensure_one_of(exclusive=True, c=lambda x: x, d=lambda x: x)
def foo(a, b):
pass

# Transform arguments.
@transform_args(a=lambda x: x * x)
def foo(a):
pass

# Bundling multiple constraints.
# Contracts run in inside out order
# i.e the one right above function will run first.
# In this case, `@ensure_args...` will be the first to run.
@transform_args(a=lambda x: x * x)
@ensure_one_of(c=lambda x: x, d=lambda x: x)
@ensure_args(a=lambda x: x > 10,
b=lambda x: hasattr(x, '__getitem__'),
c=lambda x: x < 5)
def foo(a, b, c=4, d=None):
pass


Function/method hooks.
``````````````````````

Basic function hooks to run on entering, leaving or both ways.

::

def login(root):
print "Logging in."

def logout(root):
print "Logging out"

# `login` will run before entering `home`.
# `logout` will run after exiting from `home`.
# `root` param passed to `home` will be passed to `login`, `logout`.
@enter(login)
@leave(logout)
def home(root):
print "Home page."


def tracer():
print "tracing"

# `tracer` will run both before entering `home` and after
# exiting `home`.
@around(tracer)
def inbox():
print "Inbox"

Please note that the hooks(`login` and `logout`) above are passed the arguments passed to the wrapped method(`home`).

Method hooks should be accepting the same arguments as wrapped method.


They work the same on bound functions.

::
class Foo:
def login(self):
print "Logging in."

def logout(self):
print "Logging out"

@leave(logout)
@enter(login)
def home(self, test=None):
print "Home page."

def tracer(self):
print "tracing"

@around(tracer)
def inbox(self):
print "Inbox"


Dynamic delgation.
``````````````````

::

class Foo:
def __init__(self):
self.a = 'a'
self.b = 'b'
self.c = 'c'

@delegate_to('foo_delegate', 'a', 'b')
class Bar:
def __init__(self):
self.foo_delegate = Foo()
b = Bar()
# `a` and `b` will be delegated to `Foo`.
print b.a
print b.b
# This will throw an AttributeError.
print b.c