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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 cftime_to_timestamp(date, time_unit='us'):
 """Converts cftime to timestamp since epoch in milliseconds Non-standard calendars (e.g. Julian or no leap calendars) are converted to standard Gregorian calendar. This can cause extra space to be added for dates that don't exist in the original calendar. In order to handle these dates correctly a custom bokeh model with support for other calendars would have to be defined. Args: date: cftime datetime object (or array) Returns: time_unit since 1970-01-01 00:00:00 """

    import cftime
    utime = cftime.utime('microseconds since 1970-01-01 00:00:00')
    if time_unit == 'us':
        tscale = 1
    else:
        tscale = (np.timedelta64(1, 'us')/np.timedelta64(1, time_unit))
    return utime.date2num(date)*tscale