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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 dateof(tag_name, tags):
 """Given a list of tags, returns the datetime of the tag with the given name; Otherwise None."""

    for tag in tags:
        if tag['name'] == tag_name:
            commit = read_url(tag['commit']['url'])
            return parse_timestamp(commit['commit']['committer']['date'])
    return None