Human readable data rates

speed.py

class Speed:
    """
    For human-readable bitrates

    >>> now = datetime.utcnow()
    >>> then = now - timedelta(seconds=4)
    >>> speed = Speed(n_bytes=200e6, start_time=then, end_time=now)  # e.g. transferring approx 200 meg in 4 seconds
    >>> print(speed)
    50000000.0 bytes/s
    >>> f'{speed:MBps}'  # specify units in the format mini language
    '47.6837158203125 MBps'
    >>> f'{speed:Gbps}'
    '0.4 Gbps'
    >>> f'{speed:8,kBps}'  # the segment before the unit gets passed up to default formatter
    '48,828.125 kBps'
    """

    divisors = {
        'kbps': 1_000 / 8,
        'Mbps': 1_000_000 / 8,
        'Gbps': 1_000_000_000 / 8,
        'kBps': 1_024,
        'MBps': 1_048_576,
        'GBps': 1_073_741_824,
    }

    def __init__(self, n_bytes, start_time, end_time):
        try:
            self.bytes_per_second = n_bytes / (end_time-start_time).total_seconds()
        except ZeroDivisionError:
            self.bytes_per_second = float('inf')

    def __str__(self):
        return format(self)

    def __format__(self, format_spec):
        if format_spec.endswith(tuple(self.divisors)):
            format_spec, units = format_spec[:-4], format_spec[-4:]
            divisor = self.divisors[units]
        else:
            divisor = 1
            units = 'bytes/s'
        return f'{self.bytes_per_second/divisor:{format_spec}} {units}'