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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 _validate_domains(domains):
 """Check that all domains specified in the settings was provided in the options."""

        missing = set(settings.TRANSLATION_DOMAINS.keys()) - set(domains.keys())
        if missing:
            print('The following domains have been set in the configuration, '
                  'but their sources were not provided, use the `--source` '
                  'option to specify their sources: {domains}'.format(domains=', '.join(missing)))
            sys.exit(1)