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

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#!/user/bin/env python

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

classNull:
def__init__(self, *args, **kwargs):
"Ignore parameters."
returnNone

def__call__(self, *args, **kwargs):
"Ignore method calls."
returnself

def__getattr__(self, mname):
"Ignore attribute requests."
returnself

def__setattr__(self, name, value):
"Ignore attribute setting."
returnself

def__delattr__(self, name):
"Ignore deleting attributes."
returnself

def__repr__(self):
"Return a string representation."
return"<Null>"

def__str__(self):
"Convert to a string and return it."
return"Null"

deftest():
"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'

deln.attr1
deln.attr1.attr2.attr3

# representation and conversion to a string

assertrepr(n) =='<Null>'
assertstr(n) =='Null'

if__name__=='__main__':
test()