What are some other way to rewrite this if block?

[Steven D'Aprano]

On Mon, 18 Mar 2013 19:26:16 +0530, Santosh Kumar wrote:

> This simple script is about a public transport, here is the code:
> 
> def report_status(should_be_on, came_on):
>     if should_be_on < 0.0 or should_be_on > 24.0 or came_on < 0.0 or
> came_on > 24.0:
>         return 'time not in range'
>     elif should_be_on == came_on:
>         return 'on time'
>     elif should_be_on > came_on:
>         return 'early'
>     elif should_be_on < came_on:
>         return 'delayed'
>     else:
>         return 'something might be wrong'


Untested, but something like this should work. It adjusts for the times 
which fall either side of midnight, it optionally allows for some "slop" 
in deciding whether an arrival was on time or not (defaults to 0).


def report(scheduled, actual, slop=0.0):
    """Report whether actual time of arrival is on time, late, early 
    or cancelled.

    Pass actual=None for cancelled services, otherwise both scheduled and 
    actual must be given as float hours between 0 and 24. E.g. to indicate
    a time of 06:30, pass 6.5.

    Optional argument slop is a non-negative time in hours which services
    are allowed to be late or early and still count as "on time". E.g. if 
    a service is allowed to arrive with two minutes either side of the
    scheduled time and still count as on time, pass slop=2.0/60. The slop
    defaults to 0.0.

    """
    if not 0 <= scheduled < 24:
        raise ValueError('scheduled time out of range')
    if not 0 <= slop < 24:
        raise ValueError('slop out of range')
    if actual is None:
        return "service cancelled"
    if not 0 <= actual < 24:
        raise ValueError('actual arrival time out of range')
    diff = actual - scheduled
    # Adjust for discontinuity around midnight. We assume that arrivals
    # are never more than 12 hours away from their scheduled times.
    if diff < -12:
        # For example, scheduled=23:55, actual=00:05 gives diff of -23:50
        diff += 24
    elif diff > 12:
        diff -= 24
    if diff < -slop:
        return "early"
    elif diff > slop:
        return "late"
    else:
        return "on time"


One disadvantage with the function as written is that you have to give 
times as floats between 0 and 24, instead of a more natural HH:MM syntax. 
For example, 11:07am would have to be given as 11.116666666666667. 

Another weakness is that any slop allowance is symmetrical (e.g. you 
can't allow trains to arrive up to one minute early or five minutes late 
to be counted as "on time", the two figures have to be equal).

A third weakness is that you can't allow for arrivals more than 12 hours 
early or late.



> I am looking forward of make the line starting with `if` short.

:-)



-- 
Steven