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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 Calls(self, conditions=None):
 """Find the methods that evaluate data that meets this condition. Args: conditions: A tuple of (artifact, os_name, cpe, label) Returns: A list of methods that evaluate the data. """

    results = set()
    if conditions is None:
      conditions = [None]
    for condition in conditions:
      for c in self.Match(*condition):
        results.update(self._registry.get(c, []))
    return results