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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 _revision_url(cls, rev, branch, target_platform):
 """Retrieve the URL for revision based builds"""

        namespace = 'gecko.v2.mozilla-' + branch + '.revision.' + rev
        product = 'mobile' if 'android' in target_platform else 'firefox'
        return cls.URL_BASE + '/task/' + namespace + '.' + product + '.' + target_platform