parameters: (pat)
docstring: Accepts a pytree Pattern Node and returns a set
          of the pattern types which will match first.
docstring_summary: Accepts a pytree Pattern Node and returns a set
          of the pattern types which will match first.
docstring_tokens: Accepts a pytree Pattern Node and returns a set of the pattern types which will match first .
function: def _get_head_types(pat):
      """ Accepts a pytree Pattern Node and returns a set
          of the pattern types which will match first. """
  
      if isinstance(pat, (pytree.NodePattern, pytree.LeafPattern)):
          # NodePatters must either have no type and no content
          #   or a type and content -- so they don't get any farther
          # Always return leafs
          if pat.type is None:
              raise _EveryNode
          return set([pat.type])
  
      if isinstance(pat, pytree.NegatedPattern):
          if pat.content:
              return _get_head_types(pat.content)
          raise _EveryNode # Negated Patterns don't have a type
  
      if isinstance(pat, pytree.WildcardPattern):
          # Recurse on each node in content
          r = set()
          for p in pat.content:
              for x in p:
                  r.update(_get_head_types(x))
          return r
  
      raise Exception("Oh no! I don't understand pattern %s" %(pat))
function_tokens: def _get_head_types ( pat ) : if isinstance ( pat , ( pytree . NodePattern , pytree . LeafPattern ) ) : # NodePatters must either have no type and no content #   or a type and content -- so they don't get any farther # Always return leafs if pat . type is None : raise _EveryNode return set ( [ pat . type ] ) if isinstance ( pat , pytree . NegatedPattern ) : if pat . content : return _get_head_types ( pat . content ) raise _EveryNode # Negated Patterns don't have a type if isinstance ( pat , pytree . WildcardPattern ) : # Recurse on each node in content r = set ( ) for p in pat . content : for x in p : r . update ( _get_head_types ( x ) ) return r raise Exception ( "Oh no! I don't understand pattern %s" % ( pat ) )