parameters: (self, *args, **kw)
docstring: Execute this event, but only if it has not been
          executed already for this collection.
docstring_summary: Execute this event, but only if it has not been
          executed already for this collection.
docstring_tokens: Execute this event but only if it has not been executed already for this collection .
function: def exec_once(self, *args, **kw):
          """Execute this event, but only if it has not been
          executed already for this collection."""
  
          if not self._exec_once:
              self._exec_once_impl(False, *args, **kw)
function_tokens: def exec_once ( self , * args , * * kw ) : if not self . _exec_once : self . _exec_once_impl ( False , * args , * * kw )