(self, key)
return sympify(key) in self._dict
D.__contains__(k) -> True if D has a key k, else False
D.__contains__(k) -> True if D has a key k, else False
D . __contains__ ( k ) - > True if D has a key k else False
def __contains__(self, key):
        '''D.__contains__(k) -> True if D has a key k, else False'''
        return sympify(key) in self._dict
def __contains__ ( self , key ) : return sympify ( key ) in self . _dict