<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def regenerate_prefixes(self, *args):
 """Regenerate the cache of command prefixes based on nick etc."""

        nick = self.controller.client.user.nick
        self.prefixes = set([
            nick + ": ",
            nick + ", ",
            nick + " - ",
        ])
        # Include lower-case versions as well, but not caps
        self.prefixes.update([p.lower() for p in self.prefixes])
        if self.sigil:
            self.prefixes.add(self.sigil)