845     def _findsymbolsused(self, tree, syms):

   846         if not tree:

   847             return

   848         op = tree[0]

   849         if op == 'symbol':

   850             s = tree[1]

   851             if s in syms[0]:

   852                 return # avoid recursion: s -> cache[s] -> s

   853             syms[0].add(s)

   854             if s in self.cache or s in self._map:

   855                 # s may be a reference for named template

   856                 self._findsymbolsused(self.load(s), syms)

   857             return

   858         if op in {'integer', 'string'}:

   859             return

   860         # '{arg|func}' == '{func(arg)}'

   861         if op == '|':

   862             syms[1].add(getsymbol(tree[2]))

   863             self._findsymbolsused(tree[1], syms)

   864             return

   865         if op == 'func':

   866             syms[1].add(getsymbol(tree[1]))

   867             self._findsymbolsused(tree[2], syms)

   868             return

   869         for x in tree[1:]:

   870             self._findsymbolsused(x, syms)

   871 

   872     def symbolsuseddefault(self):

   873         """Look up (keywords, filters/functions) referenced from the default

   874         unnamed template

   875 

   876         This may load additional templates from the map file.

   877         """

   878         return self.symbolsused('')

   879 

   880     def symbolsused(self, t):

   881         """Look up (keywords, filters/functions) referenced from the name

   882         template 't'

   883 

   884         This may load additional templates from the map file.

   885         """

   886         syms = (set(), set())

   887         self._findsymbolsused(self.load(t), syms)

   888         return syms

   889