RFE: change bool(datetime.time(0, 0, 0)) to evaluate as True

[LakinWecker]

BPO	13936

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2014-03-20.23:02:51.235>
created_at = <Date 2012-02-03.20:43:16.223>
labels = ['3.8', 'type-feature', 'library']
title = 'RFE: change bool(datetime.time(0, 0, 0)) to evaluate as True'
updated_at = <Date 2021-11-04.14:30:38.369>
user = 'https://bugs.python.org/LakinWecker'

bugs.python.org fields:

activity = <Date 2021-11-04.14:30:38.369>
actor = 'eryksun'
assignee = 'none'
closed = True
closed_date = <Date 2014-03-20.23:02:51.235>
closer = 'python-dev'
components = ['Library (Lib)']
creation = <Date 2012-02-03.20:43:16.223>
creator = 'Lakin.Wecker'
dependencies = []
files = []
hgrepos = []
issue_num = 13936
keywords = []
message_count = 51.0
messages = ['152556', '152557', '152558', '152559', '152560', '152561', '152562', '152563', '152564', '152565', '152567', '176475', '212732', '212738', '212743', '212771', '212777', '212778', '212779', '212782', '212783', '212784', '212785', '212786', '212787', '212788', '212789', '212790', '212791', '212798', '212799', '212801', '212806', '212807', '212871', '212873', '212877', '212879', '212880', '212881', '212883', '212884', '212886', '212892', '212904', '212911', '212915', '212916', '212921', '213434', '214299']
nosy_count = 0.0
nosy_names = []
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue13936'
versions = ['Python 3.8']

[LakinWecker]

midnight is represented by datetime.time(0,0,0). However, this time (unlike all other valid times, including datetime.time(0,0,1)) evalutes to false in if conditions:

import datetime
if datetime.time(0,0,0):
    print "datetime.time(0,0,0) is not a bug!"
else:
    print "datetime.time(0,0,0) is a bug!"

if datetime.time(0,0,1):
    print "datetime.time(0,0,1) is not a bug!"
else:
    print "datetime.time(0,0,1) is a bug!"

[LakinWecker]

I'm updating the versions to the ones that I've actually tried it on - this is not an exhaustive search at this point.

[bitdancer]

I don't think I would have ever thought of testing a datetime for its truth value. But the behavior you observe is consistent with the rest of Python: 0 is false.

I wonder if this is by design or by accident.

[LakinWecker]

Right. I've updated my code to be more correct:

instead of:

if not start_time:
    start_time = default_time

it now reads:

if start_time is None:
    start_time = default_time

which operates correctly and works fine for my case, I just thought it was odd that one time out of all of them evaluates to False. I too wonder if it's by design or not.

It's definitely not documented if it is by design.

[birkenfeld]

It must be by design -- someone has implemented a __bool__ (formerly __nonzero__) method; otherwise all objects would be true.

[birkenfeld]

BTW, "being a valid time" is not a good argument: 0, "" or False are all valid instances of their types.

[abalkin]

This is by design. I don't have a reference, but I do remember this being discussed. Suggestions for improving the documentation are welcome.

[tim-one]

From the docs, at:

http://docs.python.org/library/datetime.html#time-objects

"""
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.
"""

[LakinWecker]

Although I find it odd, you are all correct.

It is documented. (I don't know how I missed that when I read those docs looking for that exact documentation).

It is consistent with the rest of python.

Do I close this? Do you guys? I'm fine with closing it. Thanks and sorry for the noise.

[tim-one]

It is odd, but really no odder than "zero values" of other types evaluating to false in Boolean contexts ;-) Closing as "invalid".

[LakinWecker]

Yeah - good point, and I agree.