<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_molecule(self, index=0):
 """Get a molecule from the trajectory Optional argument: | ``index`` -- The frame index [default=0] """

        return Molecule(self.numbers, self.geometries[index], self.titles[index], symbols=self.symbols)