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Confusing error message when dividing timedelta using / #45424

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Confusing error message when dividing timedelta using /#45424
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interpreter-core(Objects, Python, Grammar, and Parser dirs)type-featureA feature request or enhancement

Description

@smontanaro
smontanaro
opened on Sep 1, 2007
BPO 1083
Nosy @brettcannon, @tebeka, @mdickinson, @abalkin, @vstinner
Superseder
  • bpo-1289118: timedelta multiply and divide by floating point
    		•
    Files
  • py3k_datetime_1083.patch
    		•

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

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    GitHub fields:

    assignee = None
closed_at = <Date 2010-06-06.01:25:31.693>
created_at = <Date 2007-09-01.19:19:34.033>
labels = ['interpreter-core', 'type-feature']
title = 'Confusing error message when dividing timedelta using /'
updated_at = <Date 2010-06-06.01:25:31.690>
user = 'https://github.com/smontanaro'

    bugs.python.org fields:

    activity = <Date 2010-06-06.01:25:31.690>
actor = 'belopolsky'
assignee = 'none'
closed = True
closed_date = <Date 2010-06-06.01:25:31.693>
closer = 'belopolsky'
components = ['Interpreter Core']
creation = <Date 2007-09-01.19:19:34.033>
creator = 'skip.montanaro'
dependencies = []
files = ['8792']
hgrepos = []
issue_num = 1083
keywords = ['patch']
message_count = 10.0
messages = ['55566', '55904', '75725', '101281', '101969', '102006', '103725', '103771', '103778', '107170']
nosy_count = 7.0
nosy_names = ['brett.cannon', 'tebeka', 'mark.dickinson', 'belopolsky', 'vstinner', 'webograph', 'l0nwlf']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = None
status = 'closed'
superseder = '1289118'
type = 'enhancement'
url = 'https://bugs.python.org/issue1083'
versions = ['Python 3.2']

    Activity

    1. smontanaro commented on Sep 1, 2007

      @smontanaro
      smontanaro
      on Sep 1, 2007
      ContributorAuthor

      I discovered the hard way today that this won't work:

      >>> import datetime
>>> d = datetime.timedelta(1)
>>> d / 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'datetime.timedelta' and 'int'

      The error message is misleading, because in fact timedelta
      objects *do* support division by ints, just not with the
      / operator:

      >>> d // 2
datetime.timedelta(0, 43200)

      Is there some way the error message can be improved,
      perhaps by identifying the denominator as effectively
      a float?

    2. smontanaro
      added
      type-bugAn unexpected behavior, bug, or error
      interpreter-core(Objects, Python, Grammar, and Parser dirs)
      on Sep 1, 2007

    3. brettcannon commented on Sep 14, 2007

      @brettcannon
      brettcannon
      on Sep 14, 2007
      Member

      If you set nb_true_div on timedelta objects to delta_divide (just like
      nb_floor_div) you won't have this problem as the division will just
      work. Otherwise there is no other good way as if the divisor doesn't
      work you need to return NotImplemented, which then tries the right-hand
      object which fails, and 'object' returns the TypeError. Best you could
      do is a warning or something.

      But it might make sense to only set it on nb_true_div as the division
      does not round anything.

    4. vstinner commented on Nov 11, 2008

      @vstinner
      vstinner
      on Nov 11, 2008
      Member
      The current behaviour is consistent with the integer divison:
>>> 21 // 10
2
>>> timedelta(microseconds=20) // 10
datetime.timedelta(0, 0, 2)

Whereas int/int gives float:
>>> 21 / 10
2.1000000000000001
>> timedelta(microseconds=20) / 1
...
TypeError: unsupported operand type(s) for /: ...

      Now in the real world, it's hard to understand that the operator //
      should be used instead of /. So timedelta()/int might be an alias to
      timedelta()//int.

    5. tebeka commented on Mar 18, 2010

      @tebeka
      tebekamannequin
      on Mar 18, 2010
      Mannequin

      I see the same problem when "from __future__ import division" on the 2.x series. Seem like the timedelta objects is missing the __truediv__ method.

    6. l0nwlf commented on Mar 31, 2010

      @l0nwlf
      l0nwlfmannequin
      on Mar 31, 2010
      Mannequin

      I do not understand why python2.7 is marked in Version tag ?

      I reproduced the error on 3.1 but no isues on 2.7

      06:39:30 l0nwlf-MBP:data $ python2.7
Python 2.7a4+ (trunk:78750, Mar  7 2010, 08:09:00) 
[GCC 4.2.1 (Apple Inc. build 5646) (dot 1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import datetime
>>> d = datetime.timedelta(1)
>>> d / 2
datetime.timedelta(0, 43200)
>>> d // 2
datetime.timedelta(0, 43200)
>>> 

06:41:13 l0nwlf-MBP:data $ python3.1
Python 3.1.1 (r311:74480, Mar 21 2010, 20:21:46) 
[GCC 4.2.1 (Apple Inc. build 5646) (dot 1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import datetime
>>> d = datetime.timedelta(1)
>>> d / 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'datetime.timedelta' and 'int'
>>> d // 2
datetime.timedelta(0, 43200)
>>>

    7. tebeka commented on Mar 31, 2010

      @tebeka
      tebekamannequin
      on Mar 31, 2010
      Mannequin

      It's marked on 2.7 due to the following (this is svn 79528)

      >>> from datetime import timedelta
>>> d = timedelta(1)
>>> d / 2
datetime.timedelta(0, 43200)
>>> d // 2
datetime.timedelta(0, 43200)
>>> from __future__ import division
>>> d / 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'datetime.timedelta' and 'int'
>>>

    8. AlexanderBelopolsky commented on Apr 20, 2010

      @AlexanderBelopolsky
      AlexanderBelopolskymannequin
      on Apr 20, 2010
      Mannequin

      This is certainly not a bug, so I don't think targeting 2.7 is appropriate. I have explained in a comment on bpo-2706 (see msg75917) why I believe true division of timedelta by int should not be supported. In short, true division of timedelta by int is supposed to return fractional number of microseconds, but python lacks a type that can represent it.

    9. mdickinson commented on Apr 20, 2010

      @mdickinson
      mdickinson
      on Apr 20, 2010
      Member

      I think it's fine to do the division and round the result to the nearest whole number of microseconds. I don't see any good reason for disallowing timedelta / int (or even timedelta / float).

    10. mdickinson
      added
      type-featureA feature request or enhancement
      and removed
      type-bugAn unexpected behavior, bug, or error
      on Apr 20, 2010

    11. smontanaro commented on Apr 20, 2010

      @smontanaro
      smontanaro
      on Apr 20, 2010
      ContributorAuthor

      Mark> I think it's fine to do the division and round the result to the
      Mark> nearest whole number of microseconds.

      Right. Just think of a timedelta as a floating point number of seconds with
      very limited precision (1e-6 seconds).

    12. abalkin commented on Jun 6, 2010

      @abalkin
      abalkin
      on Jun 6, 2010
      Member

      Closing as duplicate of bpo-1289118. Division of timedelta by integer is supported in py3k since r81625.

    13. abalkin
      closed this as completedon Jun 6, 2010
    14. ezio-melotti
      transferred this issue fromon Apr 10, 2022
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