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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 coerce(value):
 """ Turns value into a string """

        if isinstance(value, StringCell):
            return value
        elif isinstance(value, (str, unicode)):
            return StringCell(value)
        else:
            raise CoercionFailure("Cannot coerce %s to StringCell" % (value))