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#!/usr/bin/env python

# -*- coding: utf-8 -*-

"""http://code.activestate.com/recipes/68205-null-object-design-pattern/"""

class Null:

def __init__(self, *args, **kwargs):

"""Ignore parameters."""

return None

def __call__(self, *args, **kwargs):

"""Ignore method calls."""

return self

def __getattr__(self, mname):

"""Ignore attribute requests."""

return self

def __setattr__(self, name, value):

"""Ignore attribute setting."""

return self

def __delattr__(self, name):

"""Ignore deleting attributes."""

return self

def __repr__(self):

"""Return a string representation."""

return "<Null>"

def __str__(self):

"""Convert to a string and return it."""

return "Null"

def test():

"""

Perform some decent tests, or rather: demos.

>>> print(Null())

Null

>>> print(Null('value'))

Null

>>> n= Null('vale',param='value')

>>> print(n)

Null

>>> n()

<Null>

>>> n('value')

<Null>

>>> n('value', param='value')

<Null>

>>> print(n)

Null

"""

# constructing and calling

#n = Null()

#print(n)

#n = Null('value')

#print(n)

n = Null('value', param='value')

#print(n)

n()

#n('value')

#n('value', param='value')

#print(n)

# attribute handling

n.attr1

print('attr1', n.attr1)

n.attr1.attr2

n.method1()

n.method1().method2()

n.method('value')

n.method(param='value')

n.method('value', param='value')

n.attr1.method1()

n.method1().attr1

n.attr1 = 'value'

n.attr1.attr2 = 'value'

del n.attr1

del n.attr1.attr2.attr3

# representation and conversion to a string

assert repr(n) == '<Null>'

assert str(n) == 'Null'

if __name__ == '__main__':

test()

import doctest

doctest.testmod()

### OUTPUT ###

# ('attr1', <Null>)