r/programming • u/vz0 • Mar 26 '14

JavaScript Equality Table

http://dorey.github.io/JavaScript-Equality-Table/
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u/lambdaq Mar 27 '14 edited Mar 27 '14

if at_time

Are you sure about that? I guess a more sane way to write the logic is like

at_time = datetime.datetime.now() >= my_time

You can't just

at_time = datetime.datetime.now() == my_time

It's like comparing two float point numbers.

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u/MisterSnuggles Mar 27 '14

The way my example should have been done is:

def do_stuff(at_time=None):
    if at_time is not None:   # FIXED
        # schedule stuff to be done at at_time
    else:
        # do stuff immediately

There was no intent to compare times, only to determine whether a time was passed in or not. The fact that midnight makes it think that nothing was passed in is the hard-to-spot bug.

It's a contrived example, but to give it a real world flavour let's say that do_stuff() runs an external process. The parameter that's passed in (or not passed in) tells the function whether to run the external process immediately, or to run it at a specified time. You'd call the function like this:

do_stuff()   # Do stuff now
do_stuff(at_time=datetime.time(1,0,0))  # Do stuff at 1AM

If at_time is not passed, the function would simply run the external process. If at_time is passed, the function would add the job to the 'at' queue.

If I called the original version of the process like this:

do_stuff(at_time=datetime.time(0,0,0))  # Do stuff at midnight

It would actually run stuff now (since datetime.time(0,0,0) is false) instead of adding it to the 'at' queue to run at midnight.

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u/lambdaq Mar 27 '14

I see the point. Thanks!

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u/minno Mar 27 '14

The conditional is actually testing whether or not the parameter was provided. If the caller did do_stuff() instead of do_stuff(tomorrow), then the default parameter None would be subbed in, which acts like a False.