parameters: (self, key)
return_statement: return key in self._mapping
docstring: Check if a key exists in this cache.
docstring_summary: Check if a key exists in this cache.
docstring_tokens: Check if a key exists in this cache .
function: def __contains__(self, key):
          """Check if a key exists in this cache."""
          return key in self._mapping
function_tokens: def __contains__ ( self , key ) : return key in self . _mapping