[issue33941] datetime.strptime not able to recognize invalid date formats

[Paul Ganssle]

Change by Paul Ganssle :


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nosy: +p-ganssle

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[issue33941] datetime.strptime not able to recognize invalid date formats

[Chris Wilcox]

Chris Wilcox  added the comment:

I looked a bit at _strptime.py and the corresponding tests and thought I would 
share my notes.

The regular expressions clearly allow non-zero padded values for both %d and %m 
matches. There is one test where the following is run: time.strptime("Mar 1", 
"%b %d"). So it seems intentional that %d and %m allow non-zero padded values.

It also just occurred to me that the example '181223' isn't ambiguous as %Y 
requires 4 digits and months cannot be more than 12. So it seems to me this 
could only be Y=1812,M=2,D=3.

There do exist cases in which they are truly ambiguous for non-zero padded 
values. For instance, 2018111 could potentially be 2018-Nov-1 or 2018-Jan-11. 
Python will deterministically take the most possible for the next value, so 
this will be November 11, 2018. Though, there is really no reason I can figure 
that can be assumed.

The edits required to stop allowing non-zero padded values were pretty 
straightforward and only one unit test (one that verifies 'Mar 1' comes after 
'Feb 29') had to be altered. That may point more to a need to add additional 
tests though than an endorsement that no one is using single digit day or month 
values.

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[issue33941] datetime.strptime not able to recognize invalid date formats

[Ned Deily]

Change by Ned Deily :


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nosy: +belopolsky

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[issue33941] datetime.strptime not able to recognize invalid date formats

[Chris Wilcox]

Chris Wilcox  added the comment:

As %m and %d denote zero padded forms of month and day it seems to me this 
shouldn't match. Executing a small c program `char* ret = strptime("181223", 
"%Y%m%d", );` confirms that this is considered invalid to c. The datetime 
docs indicate that the behavior should match C89 so I would expect python to 
return ValueError here as well. 
https://docs.python.org/3/library/datetime.html#strftime-strptime-behavior

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components: +Library (Lib) -Tests
nosy: +crwilcox
versions: +Python 2.7

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[issue33941] datetime.strptime not able to recognize invalid date formats

[Raghunath Lingutla]

New submission from Raghunath Lingutla :

Can not recognize invalid date values for %Y%m%d, %y%m%d, %Y%m%d %H:%M and few 
more formats. In Java we have setLenient option which help us to validate to 
pattern and convert only valid formats
Ex: datetime.strptime('181223', '%Y%m%d') 
For above input I am getting output as 1812-02-03 00:00:00 but expected output 
is error as ValueError: time data '181223' does not match format '%Y%m%d'

I tested below mentioned 4 modules. All modules giving same output

1) datetime.strptime

2) timestring.Date

3) parser.parse from dateutil

4) dateparser.parse

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components: Tests
messages: 320233
nosy: Raghunath Lingutla
priority: normal
severity: normal
status: open
title: datetime.strptime not able to recognize invalid date formats
type: behavior
versions: Python 3.6

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