def map_values_in_place(self, f):
    for i in range(len(self._values)):
        (p, v) = self._values[i]
        self._values[i] = (p, f(v))
def map_values_in_place(self, f):
    for i in range(len(self._values)):
        (p, v) = self._values[i]
        self._values[i] = (p, f(v))