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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 b64decode_url(istr):
 """ JWT Tokens may be truncated without the usual trailing padding '=' symbols. Compensate by padding to the nearest 4 bytes. """

    istr = encode_safe(istr)
    try:
        return urlsafe_b64decode(istr + '=' * (4 - (len(istr) % 4)))
    except TypeError as e:
        raise Error('Unable to decode base64: %s' % (e))