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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_zeropoint(expnum, ccd, prefix=None, version='p'):
 """Get the zeropoint for this exposure using the zeropoint.used file created during source planting.. This command expects that there is a file called #######p##.zeropoint.used which contains the zeropoint. @param expnum: exposure to get zeropoint of @param ccd: which ccd (extension - 1) to get zp @param prefix: possible string prefixed to expsoure number. @param version: one of [spo] as in #######p## @return: zeropoint """

    uri = get_uri(expnum, ccd, version, ext='zeropoint.used', prefix=prefix)
    try:
        return zmag[uri]
    except:
        pass

    try:
        zmag[uri] = float(open_vos_or_local(uri).read())
        return zmag[uri]
    except:
        pass

    zmag[uri] = 0.0
    return zmag[uri]