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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 change_password(self, usrname, oldpwd, newpwd, callback=None):
        '''
        Change password.
        '''
        params = {'usrName': usrname,
                  'oldPwd' : oldpwd,
                  'newPwd' : newpwd,
                 }
        return self.execute_command('changePassword',
                                    params, callback=callback)