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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_registerd_func(name_or_func):
 """ get a xcorr function from a str or callable. """

    # get the function or register callable
    if callable(name_or_func):
        func = register_array_xcorr(name_or_func)
    else:
        func = XCOR_FUNCS[name_or_func or 'default']
    assert callable(func), 'func is not callable'
    # ensure func has the added methods
    if not hasattr(func, 'registered'):
        func = register_array_xcorr(func)
    return func