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Add Singleton design pattern example #444

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Add Singleton design pattern example #444

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17 changes: 17 additions & 0 deletions patterns/singleton.py
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"""
Singleton Pattern Example
Ensures a class has only one instance and provides a global point of access to it.
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In line with doctoring standards - could the second line of this doctoring be empty please. (add empty line)

See https://github.com/faif/python-patterns/blob/master/patterns/structural/facade.py for an example of a good docString. Unfortunately there are many poor examples around.

"""

class Singleton:
_instance = None

def __new__(cls):
if not cls._instance:
cls._instance = super(Singleton, cls).__new__(cls)
return cls._instance

if __name__ == "__main__":
obj1 = Singleton()
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Also referring to the facade documentation lines 94-97, this repo uses doctests to establish testing.

Could you follow the same pattern to demonstrate the principle you are demonstrating here..

obj2 = Singleton()
print("Are obj1 and obj2 the same?", obj1 is obj2)