def step(self):
    'Take a simulation step.'
    for body in self.bodies.values():
        body.update()
    for constraint in self.constraints.values():
        constraint.update()
    self.physics.step()
    self._num_steps += 1
Take a simulation step.
def step(self):
    
    for body in self.bodies.values():
        body.update()
    for constraint in self.constraints.values():
        constraint.update()
    self.physics.step()
    self._num_steps += 1