25     """Subclass of ValueError raised by TopologicalSorter.prepare if cycles
70         Raises ValueError if called after "prepare".
73             raise ValueError("Nodes cannot be added after a call to prepare()")
84     def prepare(self):  member in TopologicalSorter
93             raise ValueError("cannot prepare() more than once")
114         Raises ValueError if called without calling "prepare" previously.
117             raise ValueError("prepare() must be called first")
140         Raises ValueError if called without calling "prepare" previously.
143             raise ValueError("prepare() must be called first")
157         graph by using "add" or if called without calling "prepare" previously or if
162             raise ValueError("prepare() must be called first")
239         Using this method does not require to call "prepare" or "done". If any
242         self.prepare()