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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_uri(expnum, ccd=None, version='p', ext=FITS_EXT, subdir=None, prefix=None):
 """ Build the uri for an OSSOS image stored in the dbimages containerNode. :rtype : basestring expnum: CFHT exposure number ccd: CCD in the mosaic [0-35] version: one of p,s,o etc. dbimages: dbimages containerNode. @type subdir: str @param expnum: int @param ccd: @param version: @param ext: @param subdir: @param prefix: """

    if subdir is None:
        subdir = str(expnum)
    if prefix is None:
        prefix = ''
    uri = os.path.join(DBIMAGES, subdir)

    if ext is None:
        ext = ''
    elif len(ext) > 0 and ext[0] != '.':
        ext = '.' + ext

    if version is None:
        version = ''

    if ccd is None:
        uri = os.path.join(uri,
                           '%s%s%s%s' % (prefix, str(expnum),
                                         version,
                                         ext))
    else:
        ccd = str(ccd).zfill(2)
        uri = os.path.join(uri,
                           'ccd{}'.format(ccd),
                           '%s%s%s%s%s' % (prefix, str(expnum),
                                           version,
                                           ccd,
                                           ext))

    return uri