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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_tag(expnum, key):
 """given a key, return the vospace tag value. @param expnum: Number of the CFHT exposure that a tag value is needed for @param key: The process tag (such as mkpsf_00) that is being looked up. @return: the value of the tag @rtype: str """


    uri = tag_uri(key)
    force = uri not in get_tags(expnum)
    value = get_tags(expnum, force=force).get(uri, None)
    return value