human
Complete the below
def addGradientListToDocstring():

    ''''Decorator to add list of current pre-defined gradients to the end of a function docstring.'
    '''

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Write me a the Python code you requested?
assistant
#Here is the Python code you requested.
    def dec(fn):
        if (fn.__doc__ is not None):
            fn.__doc__ = (fn.__doc__ + str(Gradients.keys()).strip('[').strip(']'))
        return fn
    return dec