Documenting Functions : Documentation « Function « Python Tutorial

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# If you put a string at the beginning of a function, it is stored as part of the function and is called a docstring. 
# __doc__ is a function attribute. 
# The double underscores mean that this is a special attribute. 

def square(x):
   'Calculates the square of the number x.'
   return x*x 

# The docstring may be accessed like this: 
print square.__doc__


help(square)