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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 push(self):
 """Push the changes to the remote repository. Usage: payu push This command pushes local runlog changes to the remote runlog repository, currently named `payu`, using the SSH key associated with this experiment. For an experiment `test`, it is equivalent to the following command:: ssh-agent bash -c " ssh-add $HOME/.ssh/payu/id_rsa_payu_test git push --all payu " """

        expt_name = self.config.get('name', self.expt.name)

        default_ssh_key = 'id_rsa_payu_' + expt_name
        ssh_key = self.config.get('sshid', default_ssh_key)
        ssh_key_path = os.path.join(os.path.expanduser('~'), '.ssh', 'payu',
                                    ssh_key)

        if not os.path.isfile(ssh_key_path):
            print('payu: error: Github SSH key {key} not found.'
                  ''.format(key=ssh_key_path))
            print('payu: error: Run `payu ghsetup` to generate a new key.')
            sys.exit(-1)

        cmd = ('ssh-agent bash -c "ssh-add {key}; git push --all payu"'
               ''.format(key=ssh_key_path))
        subprocess.check_call(shlex.split(cmd), cwd=self.expt.control_path)