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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 _deprefix(line, prefix, callback=None):
 """Remove the prefix string from the beginning of line, if it exists. :param string line: A line, such as one output by GnuPG's status-fd. :param string prefix: A substring to remove from the beginning of ``line``. Case insensitive. :type callback: callable :param callback: Function to call if the prefix is found. The signature to callback will be only one argument, the ``line`` without the ``prefix``, i.e. ``callback(line)``. :rtype: string :returns: If the prefix was found, the ``line`` without the prefix is returned. Otherwise, the original ``line`` is returned. """

    try:
        assert line.upper().startswith(u''.join(prefix).upper())
    except AssertionError:
        log.debug("Line doesn't start with prefix '%s':\n%s" % (prefix, line))
        return line
    else:
        newline = line[len(prefix):]
        if callback is not None:
            try:
                callback(newline)
            except Exception as exc:
                log.exception(exc)
        return newline