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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 get_mock_personalization_dict():
 """Get a dict of personalization mock."""

    mock_pers = dict()

    mock_pers['to_list'] = [To("test1@example.com",
                                  "Example User"),
                            To("test2@example.com",
                                  "Example User")]

    mock_pers['cc_list'] = [To("test3@example.com",
                                  "Example User"),
                            To("test4@example.com",
                                  "Example User")]

    mock_pers['bcc_list'] = [To("test5@example.com"),
                             To("test6@example.com")]

    mock_pers['subject'] = ("Hello World from the Personalized "
                            "SendGrid Python Library")

    mock_pers['headers'] = [Header("X-Test", "test"),
                            Header("X-Mock", "true")]

    mock_pers['substitutions'] = [Substitution("%name%", "Example User"),
                                  Substitution("%city%", "Denver")]

    mock_pers['custom_args'] = [CustomArg("user_id", "343"),
                                CustomArg("type", "marketing")]

    mock_pers['send_at'] = 1443636843
    return mock_pers