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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 counter(self, ch, part=None):
 """Return a counter on the channel ch. ch: string or integer. The channel index number or channel name. part: int or None The 0-based enumeration of a True part to return. This has an effect whether or not the mask or filter is turned on. Raise IndexError if the part does not exist. See `Counter <https://docs.python.org/2.7/library/collections.html#counter-objects>`_ for the counter object returned. """

        return Counter(self(self._key(ch), part=part))