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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 find_tokens(self, q):
 """Find all AST nodes at the given filename, line and column."""

    found_me = []
    if hasattr(self, 'location'):
      if self.location.contains(q):
        found_me = [self]
    elif self._found_by(q):
      found_me = [self]

    cs = [n.find_tokens(q) for n in self._children()]
    return found_me + list(itertools.chain(*cs))