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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 providerIsAuthoritative(providerID, canonicalID):
 """Is this provider ID authoritative for this XRI? @returntype: bool """

    # XXX: can't use rsplit until we require python >= 2.4.
    lastbang = canonicalID.rindex('!')
    parent = canonicalID[:lastbang]
    return parent == providerID