[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

No, the bug is not fixed, and this is not easy issue. You should use 
non-integer Decimals to reproduce it. In 3.8 this emits a deprecation warning:

>>> import datetime
>>> from decimal import Decimal as D
>>> datetime.datetime.utcfromtimestamp(D(1425808327.307651))
:1: DeprecationWarning: an integer is required (got type 
decimal.Decimal).  Implicit conversion to integers using __int__ is deprecated, 
and may be removed in a future version of Python.
datetime.datetime(2015, 3, 8, 9, 52, 7)

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Rémi Lapeyre]

Change by Rémi Lapeyre :


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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Paul Ganssle]

Paul Ganssle  added the comment:

Oh actually that's my mistake. I can't reproduce the failure in the constructor 
in the Python version of the module, and also it seems to be fixed in the pure 
Python version as of at least 3.6:

Python 3.6.7 (default, Oct 25 2018, 16:11:17) 
[GCC 8.2.1 20180831] on linux
>>> import sys
>>> sys.modules['_datetime'] = None
>>> from decimal import Decimal as D
>>> from datetime import datetime
>>> datetime.utcfromtimestamp(D(123456.12345))
datetime.datetime(1970, 1, 2, 10, 17, 36, 123450)

But the truncation behavior is still present in the C version as of Python 
3.8.0a1+:

Python 3.8.0a1+ (heads/master:3766f18, Feb 11 2019, 12:52:31) 
[GCC 8.2.1 20181127] on linux
>>> from datetime import datetime
>>> from decimal import Decimal as D
>>> datetime.utcfromtimestamp(D(123456.12345))
datetime.datetime(1970, 1, 2, 10, 17, 36)


I still think we need a test for the constructor behavior, but I'm going to 
remove "easy", since we still need to fix truncation in the C version.

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keywords:  -easy

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Paul Ganssle]

Paul Ganssle  added the comment:

I'm not sure if either of these patches got merged, but at some point this was 
fixed:

Python 3.7.2 (default, Feb  9 2019, 13:18:43) 
[GCC 8.2.1 20181127] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from datetime import datetime
>>> from decimal import Decimal
>>> datetime.utcfromtimestamp(Decimal(123456.0))
datetime.datetime(1970, 1, 2, 10, 17, 36)


I recommend that someone add some regression tests to this, then we can close 
the issue.

I'm also going to mark this as "easy" since adding tests for this particular 
example should be pretty simple.

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keywords: +easy

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Steven Davidson]

Change by Steven Davidson :


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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Paul Ganssle]

Change by Paul Ganssle :


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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
assignee:  -> serhiy.storchaka
priority: normal -> low
versions: +Python 3.8 -Python 3.4, Python 3.5

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Shlomo Anglister]

Change by Shlomo Anglister :


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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Here is a patch that adds Decimal support for datetime.fromtimestamp() and 
datetime.utcfromtimestamp(). As side effect Decimal timestamps now are 
supported in few other places, e.g. in os.utime().

--
nosy: +haypo
stage: needs patch - patch review
Added file: 
http://bugs.python.org/file38736/datetime_fromtimestamp_decimal.patch

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[STINNER Victor]

STINNER Victor added the comment:

I reviewed datetime_fromtimestamp_decimal.patch.

 As side effect Decimal timestamps now are supported in few other places, e.g. 
 in os.utime().

It would be more consistent to support decimal.Decimal nowhere or everywhere. 
IMO the new _PyTime_FromSecondsObject() (very close to 
_PyTime_ObjectToDenominator, but using time_t) should also be patched.

Please add some tests for decimal.Decimal in test_time directly. Usually, I try 
to test rounding and overflow. Testing for overflow is not always possible 
because it may depend on the platform.

--

See also the PEP 410: PEP 410 - Use decimal.Decimal type for timestamps. The 
PEP was rejected. The compromise was a new timestamp format for os.utime(): a 
number of nanoseconds since the UNIX epoch (1970-01-01). I partially 
implemented a private API for this PEP in the issue #22117: the new _PyTime_t 
is a number of timestamp using an arbitrary resolution (currently, it's a 
number of nanoseconds using a 64-bit signed integer type).

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

The problem is that the Decimal *was* supported in 2.7. So this issue can be 
considered not as adding new feature, but as fixing a regression. But changes 
are too large for just bugfix.

 It would be more consistent to support decimal.Decimal nowhere or 
 everywhere. IMO the new _PyTime_FromSecondsObject() (very close to 
 _PyTime_ObjectToDenominator, but using time_t) should also be patched.

Will add Decimal support in all functions in Python/pytime.c that support 
floats.

 Please add some tests for decimal.Decimal in test_time directly. Usually, I 
 try to test rounding and overflow. Testing for overflow is not always 
 possible because it may depend on the platform.

Will do.

 Is the patch context insensitive?

No, the patch is context sensitive. I think the end user is responsible to set 
an appropriate context if it want to create a datetime from Decimal timestamp. 
At least until we add functions that return Decimal.

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Stefan Krah]

Stefan Krah added the comment:

I think we should try to avoid depending on global state in
the stdlib, at least in new code.  Also, if something is not
really a decimal computation, Decimal itself tries to ignore
the context (like Decimal.__repr__).

At least I would expect this datetime function to be context
independent.

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Stefan Krah]

Stefan Krah added the comment:

I just looked at this very briefly: Is the patch context insensitive?

IOW, do things still work if you change the thread-local context:

from decimal import *
c = getcontext()
c.prec = 1
c.Emax = 1
c.Emin = -1

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Serhiy Storchaka]

Changes by Serhiy Storchaka storch...@gmail.com:


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stage: needs patch - patch review

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

The fix for Python implementation LGTM, but a fix for C implementation is 
needed too.

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stage: patch review - needs patch

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[Serhiy Storchaka]

New submission from Serhiy Storchaka:

First, datetime.utcfromtimestamp() drops fractional part of Decimal argument:

 import datetime
 from decimal import Decimal as D
 datetime.datetime.utcfromtimestamp(1425808327.307651)
datetime.datetime(2015, 3, 8, 9, 52, 7, 307651)
 datetime.datetime.utcfromtimestamp(D(1425808327.307651))
datetime.datetime(2015, 3, 8, 9, 52, 7)

Second, it works only with C implementation. With Python implementation 
Decimals are not supported at all.

 del sys.modules['datetime']
 sys.modules['_datetime'] = None
 import datetime
 datetime.datetime.utcfromtimestamp(D(1425808327.307651))
Traceback (most recent call last):
  File stdin, line 1, in module
  File /usr/lib/python3.4/datetime.py, line 1374, in utcfromtimestamp
t, frac = divmod(t, 1.0)
TypeError: unsupported operand type(s) for divmod(): 'decimal.Decimal' and 
'float'

In 2.7 Decimals are accepted and are not truncated.

 import datetime
 from decimal import Decimal as D
 datetime.datetime.utcfromtimestamp(D(1425808327.307651))
datetime.datetime(2015, 3, 8, 9, 52, 7, 307651)

So this can be considered as a regression.

--
components: Library (Lib)
messages: 237527
nosy: belopolsky, lemburg, serhiy.storchaka
priority: normal
severity: normal
status: open
title: Inconsistency in datetime.utcfromtimestamp(Decimal)
type: behavior
versions: Python 3.4, Python 3.5

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[issue23607] Inconsistency in datetime.utcfromtimestamp(Decimal)

[SilentGhost]

SilentGhost added the comment:

Here is the python-only fix that eliminates TypeError and produces correct 
number of milliseconds. The problem with C implementation lies in 
_PyTime_ObjectToDenominator function where there is an explicit check for a 
float. This check could be relaxed to include decimals as the rest of the code 
seem to work fine with decimal. I'm not entirely sure how that could be done 
though.

--
keywords: +patch
nosy: +SilentGhost
stage:  - needs patch
Added file: http://bugs.python.org/file38388/issue23607_python.diff

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