[Python-checkins] bpo-30516: Fix documentation issue with -timedelta in datetime (GH-7348)

Wed Jul 4 14:42:09 EDT 2018

https://github.com/python/cpython/commit/5b6e49a1393b3e2313471696e3568e26296137b4
commit: 5b6e49a1393b3e2313471696e3568e26296137b4
branch: master
author: Farhaan Bukhsh <farhaan.bukhsh at gmail.com>
committer: Alexander Belopolsky <abalkin at users.noreply.github.com>
date: 2018年07月04日T19:42:05+01:00
summary:
bpo-30516: Fix documentation issue with -timedelta in datetime (GH-7348)
This commit fixes the -timedelta overfllow issue not documented properly.
Signed-off-by: Farhaan Bukhsh <farhaan.bukhsh at gmail.com>
files:
M Doc/library/datetime.rst

diff --git a/Doc/library/datetime.rst b/Doc/library/datetime.rst
index 1ac2570eae5a..53c181c4014a 100644
--- a/Doc/library/datetime.rst
+++ b/Doc/library/datetime.rst
@@ -241,7 +241,7 @@ Supported operations:
 +--------------------------------+-----------------------------------------------+
 | ``t1 = t2 - t3`` | Difference of *t2* and *t3*. Afterwards *t1* |
 | | == *t2* - *t3* and *t2* == *t1* + *t3* are |
-| | true. (1) |
+| | true. (1)(6) |
 +--------------------------------+-----------------------------------------------+
 | ``t1 = t2 * i or t1 = i * t2`` | Delta multiplied by an integer. |
 | | Afterwards *t1* // i == *t2* is true, |
@@ -317,6 +317,11 @@ Notes:
 >>> print(_)
 -1 day, 19:00:00
 
+(6)
+ The expression ``t2 - t3`` will always be equal to the expression ``t2 + (-t3)`` except
+ when t3 is equal to ``timedelta.max``; in that case the former will produce a result
+ while the latter will overflow.
+
 In addition to the operations listed above :class:`timedelta` objects support
 certain additions and subtractions with :class:`date` and :class:`.datetime`
 objects (see below).
@@ -513,8 +518,6 @@ Notes:
 :const:`MINYEAR` or larger than :const:`MAXYEAR`.
 
 (2)
- This isn't quite equivalent to date1 + (-timedelta), because -timedelta in
- isolation can overflow in cases where date1 - timedelta does not.
 ``timedelta.seconds`` and ``timedelta.microseconds`` are ignored.
 
 (3)
@@ -961,8 +964,6 @@ Supported operations:
 Computes the datetime2 such that datetime2 + timedelta == datetime1. As for
 addition, the result has the same :attr:`~.datetime.tzinfo` attribute as the input
 datetime, and no time zone adjustments are done even if the input is aware.
- This isn't quite equivalent to datetime1 + (-timedelta), because -timedelta
- in isolation can overflow in cases where datetime1 - timedelta does not.
 
 (3)
 Subtraction of a :class:`.datetime` from a :class:`.datetime` is defined only if
