def pre_step(self, ctxt, step, idx):
return None<EOL>
Called prior to executing a step.

:param ctxt: An instance of ``timid.context.Context``.
:param step: An instance of ``timid.steps.Step`` describing
             the step to be executed.
:param idx: The index of the step in the list of steps.

:returns: A ``True`` value if the step is to be skipped.  Any
          ``False`` value (including ``None``) will result in
          the step being executed as normal.