python-patterns/null.py at master · Pythoning/python-patterns · GitHub

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#!/user/bin/env python

"""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."""

# 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()

python-patterns/null.py at master · Pythoning/python-patterns · GitHub

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