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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def signature(self):
 """Gets completion or call signature information for the current cursor."""

        #We can't really do anything sensible without the name of the function
        #whose signature we are completing.
        iexec, execmod = self.context.parser.tree_find(self.context.el_name, 
                                              self.context.module, "executables")
        if iexec is None:
            #Look in the interfaces next using a tree find as well
            iexec, execmod = self.context.parser.tree_find(self.context.el_name, self.context.module,
                                                  "interfaces")
        if iexec is None:
            return []

        return self._signature_index(iexec)