Please reconsider the Boolean evaluation of midnight
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Please reconsider the Boolean evaluation of midnight
1–10 of 218 posts
Re: Please reconsider the Boolean evaluation of midnight
#2I just got bit by this a few days ago. I was creating an event scheduling system that uses either repeating entries with a datetime.time, or one time entries with a datetime.datetime. I had code that said "if start_time" to see which it was, and discovered later that midnight evaluates to false. It's not the best idea.
Re: Please reconsider the Boolean evaluation of midnight
#3[deleted]
Re: Please reconsider the Boolean evaluation of midnight
#4Off the top of my head I can't think of a reason to check if a date exists, but I would certainly expect midnight to be truthy if I found a reason.
Re: Please reconsider the Boolean evaluation of midnight
#5Off the top of my head I can't think of a reason to check if a date exists, but I would certainly expect midnight to be truthy if I found a reason.
In Django you might have a nullable TimeField and check if it's set via "if obj.time_field".
Re: Please reconsider the Boolean evaluation of midnight
#6Off the top of my head I can't think of a reason to check if a date exists, but I would certainly expect midnight to be truthy if I found a reason.
What about optional date fields in a Django application?
Re: Please reconsider the Boolean evaluation of midnight
#7While I agree this is surprising behavior and I wouldn't design an API this way, it is documented behavior. From the docs:
"in Boolean contexts, a time object is considered to be true if and only if, after converting it to minutes and subtracting utcoffset() (or 0 if that’s None), the result is non-zero"
Changing at this point would possibly break code that relied on documented library behavior. That's not a responsible thing to do.
Re: Please reconsider the Boolean evaluation of midnight
#8Off the top of my head I can't think of a reason to check if a date exists, but I would certainly expect midnight to be truthy if I found a reason.
In Django you might have a nullable TimeField and check if it's set via "if obj.time_field".
I always write "if x is None", trying to be explicit.
Re: Please reconsider the Boolean evaluation of midnight
#9[deleted]
Re: Please reconsider the Boolean evaluation of midnight
#10Lots of Python objects are falsey: empty lists, empty strings, etc. So it's never a good idea to write "if " when you mean "if is not None".
This is pretty well-known, I thought.