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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 boot_time(time_format=None):
    '''
    Return the boot time in number of seconds since the epoch began.

    CLI Example:

    time_format
        Optionally specify a `strftime`_ format string. Use
        ``time_format='%c'`` to get a nicely-formatted locale specific date and
        time (i.e. ``Fri May  2 19:08:32 2014``).

        .. _strftime: https://docs.python.org/2/library/datetime.html#strftime-strptime-behavior

        .. versionadded:: 2014.1.4

    .. code-block:: bash

        salt '*' ps.boot_time
    '''
    try:
        b_time = int(psutil.boot_time())
    except AttributeError:
        # get_boot_time() has been removed in newer psutil versions, and has
        # been replaced by boot_time() which provides the same information.
        b_time = int(psutil.boot_time())
    if time_format:
        # Load epoch timestamp as a datetime.datetime object
        b_time = datetime.datetime.fromtimestamp(b_time)
        try:
            return b_time.strftime(time_format)
        except TypeError as exc:
            raise SaltInvocationError('Invalid format string: {0}'.format(exc))
    return b_time