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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 pid_max(self):
 """ Get the maximum PID value. On Linux, the value is read from the `/proc/sys/kernel/pid_max` file. From `man 5 proc`: The default value for this file, 32768, results in the same range of PIDs as on earlier kernels. On 32-bit platfroms, 32768 is the maximum value for pid_max. On 64-bit systems, pid_max can be set to any value up to 2^22 (PID_MAX_LIMIT, approximately 4 million). If the file is unreadable or not available for whatever reason, returns None. Some other OSes: - On FreeBSD and macOS the maximum is 99999. - On OpenBSD >= 6.0 the maximum is 99999 (was 32766). - On NetBSD the maximum is 30000. :returns: int or None """

        if LINUX:
            # XXX: waiting for https://github.com/giampaolo/psutil/issues/720
            try:
                with open('/proc/sys/kernel/pid_max', 'rb') as f:
                    return int(f.read())
            except (OSError, IOError):
                return None
        else:
            return None