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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 parameters(self):
 """The names of the parameters the function takes. Returns None if this completion is not a function. """

        pyname = self.pyname
        if isinstance(pyname, pynames.ImportedName):
            pyname = pyname._get_imported_pyname()
        if isinstance(pyname, pynames.DefinedName):
            pyobject = pyname.get_object()
            if isinstance(pyobject, pyobjects.AbstractFunction):
                return pyobject.get_param_names()