def f(name):
    """
    The documentation
    should have more than one lines.
    """
    print(name)


f("hello")
print(f.__doc__)

Immediately after the definition of the function, you can add a string - it can be a """ string to spread multiple lines - that will include the documentation of the function. This string can be accessed via the __doc__ (2+2 underscores) attribute of the function. Also, if you 'import' the file - as a module - in the interactive prompt of Python, you will be able to read this documentation via the help() function. help(mydocs) or help(mydocs.f) in the above case.