GeezerVison is showing github.com — time.sleep() should support objects with __float__ · Issue #79888 · python/cpython
time.sleep() should support objects with __float__ #79888Labels interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error Description
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GitHub fields:
assignee = None
closed_at = None
created_at = <Date 2019-01-10.15:58:39.782>
labels = ['interpreter-core', '3.10']
title = 'time.sleep() should support objects with __float__'
updated_at = <Date 2020-05-23.00:14:27.187>
user = 'https://github.com/jdemeyer' bugs.python.org fields:
activity = <Date 2020-05-23.00:14:27.187>
actor = 'cheryl.sabella'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2019-01-10.15:58:39.782>
creator = 'jdemeyer'
dependencies = []
files = []
hgrepos = []
issue_num = 35707
keywords = ['patch', 'patch']
message_count = 29.0
messages = ['333391', '333395', '333396', '333397', '333401', '333404', '333416', '333547', '333550', '333554', '333555', '333961', '333963', '333968', '333969', '334120', '334121', '334122', '334125', '334128', '334129', '334131', '334136', '334480', '334486', '334509', '339123', '349004', '349560']
nosy_count = 10.0
nosy_names = ['ronaldoussoren', 'ncoghlan', 'belopolsky', 'vstinner', 'serhiy.storchaka', 'jdemeyer', 'josh.r', 'p-ganssle', 'remi.lapeyre', 'AVINASH MISHRA']
pr_nums = ['11507', '11507', '11636', '11636', '11636']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue35707'
versions = ['Python 3.10'] Linked PRs
Activityjdemeyer commented on Jan 10, 2019 ContributorAuthor More actions This used to work correctly in Python 2:
class Half(object):
def __float__(self):
return 0.5
import time
time.sleep(Half())With Python 3.6, one gets instead
Traceback (most recent call last):
File "test.py", line 6, in <module>
time.sleep(Half())
TypeError: an integer is required (got type Half)AVINASHMISHRA commented on Jan 10, 2019 hey i am a total newbie to open source contribution.
can you help me understand this issue and can i help solve this issue? remilapeyre commented on Jan 10, 2019 time.sleep() is probably not the only function to have such a bug.
Maybe __int__() should default to:
def __int__(self):
return int(self.__float__())when __float__ is defined and not __int__.
Nick Coghlan suggested something similar for __int__ and __index__. remilapeyre commented on Jan 10, 2019 See bpo-33039 for the proposed change to __int__. vstinner commented on Jan 10, 2019 The problem comes from the private C function _PyTime_FromObject() of Python/pytime.c. This function must use the proper conversion to minimize the precision loss. Lib/test/test_time.py contains a lot of tests on conversions from different types and ensure that values are rounded correctly. See also my PEP-564 "Add new time functions with nanosecond resolution".
The correct code works for float and int (and maybe decimal.Decimal, I don't recall!), but it seems like it doesn't support types with __float__(). You have to explicitly cast such objects using float(value).
PyNumber_Float() can be used to convert arbitrary object to a float, but I'm not sure in which order the conversion should be tried to avoid/reduce precision loss during the conversion.
Example:
>>> x=2**53+1; x - int(float(x))
1 If we convert 'x' (int) to float, we introduce an error of 1. vstinner commented on Jan 10, 2019 PR 11507 is not directly related to this issue, see bpo-26669. But I wrote this PR when trying to fix this issue :-) jdemeyer commented on Jan 10, 2019 ContributorAuthor More actions
I'm not sure in which order the conversion should be tried to avoid/reduce precision loss during the conversion.
I would suggest the order
- __index__ to ensure exact conversion of exact integers
- __float__ to ensure correct conversion of floating-point numbers
- __int__
ncoghlan commented on Jan 13, 2019 Deriving __int__ from __float__ wouldn't be the right answer, as that can easily lead to unwanted OverflowError exceptions and other issues.
However, Jeroen's suggested order of checking __index__ then __float__ then __int__ in _PyTime_FromObject makes sense to me, as that addresses Victor's desire to use the most precise conversion available. serhiy-storchaka commented on Jan 13, 2019 This can cause a loss of precision for Decimal.
If we want to support other numerical types with loss in double rounding, the most reliable way is to represent them as fractions (x.as_integer_ratio() or (x.numerator, x.denominator)) and use precise integer arithmetic. jdemeyer commented on Jan 13, 2019 ContributorAuthor More actions
the most reliable way is to represent them as fractions (x.as_integer_ratio() or (x.numerator, x.denominator))
I don't think that we can rely on non-dunder names like that. They are not reserved names, so classes can give them any semantics that they like. This is not just hypothetical: SageMath for example uses numerator() and denominator() methods, not properties.
If you really want to go through with this, probably a special method like __as_integer_ratio__ should be defined.
Anyway, I personally consider the double rounding for time.sleep() a non-issue. We are not trying to write a precise math library here, nobody will complain about sleeping a femtosecond too long. jdemeyer commented on Jan 13, 2019 ContributorAuthor More actions
The correct code works for float and int (and maybe decimal.Decimal, I don't recall!)
Not for Decimal! In fact sleep(Decimal("0.99")) is interpreted as sleep(0) because __int__ is used to convert. jdemeyer commented on Jan 18, 2019 ContributorAuthor More actions My proposal vastly improves the situation for Decimal. I will write a PR for this and I hope that it won't be rejected just because it's not perfect. vstinner commented on Jan 18, 2019
Not for Decimal! In fact sleep(Decimal("0.99")) is interpreted as sleep(0) because __int__ is used to convert.
Oh oh. I didn't know that. It should be fixed. jdemeyer commented on Mar 29, 2019 ContributorAuthor More actions jdemeyer commented on Aug 4, 2019 ContributorAuthor More actions vstinner commented on Aug 13, 2019 ald-extrahop commented on Aug 3, 2023 If this issue is covering all the _PyTime_FromObject() uses, the change to PyLong_AsLongLong() in Python 3.10 (#80229) increased the severity. Many time functions that accept floats by design raise TypeError when passed (e.g.) a decimal.Decimal (they previously just printed a DeprecationWarning). StanFromIreland commented on Aug 12, 2025 The error message now contradicts the behavior:
>>> class Half(object):
... def __float__(self):
... return 0.5
... import time
... time.sleep(Half())
...
Traceback (most recent call last):
File "<python-input-5>", line 5, in <module>
time.sleep(Half())
~~~~~~~~~~^^^^^^^^
TypeError: 'Half' object cannot be interpreted as an integer or float
StanFromIreland commented on Dec 20, 2025 This was fixed by Serhiy in 1a2e00c:
>>> class Half(object):
... def __float__(self):
... return 0.5
... import time
... time.sleep(Half())
...
>>>
MetadataMetadatainterpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error StatusShow more project fields
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