def step(self, substeps=<NUM_LIT:2>):
<EOL>self.frame_no += <NUM_LIT:1><EOL>try:<EOL><INDENT>next(self.follower)<EOL><DEDENT>except (AttributeError, StopIteration) as err:<EOL><INDENT>self.reset()<EOL><DEDENT>
Advance the physics world by one step.

        Typically this is called as part of a :class:`pagoda.viewer.Viewer`, but
        it can also be called manually (or some other stepping mechanism
        entirely can be used).