Jinja: truncate filter can no longer truncate on the right side
Before commit #610 it was possible to do right side truncation, e.g. if one wanted to split a month name into abbreviated (3 char long) and non-abbreviated form it would be possible to achieve with:
"November"|truncate(3, True, '')
"November"|reverse|truncate(-3, True, '')|reverse
The above would produce "Nov" and "ember" due to the way how string functions work:
>>> s='123456789'
>>> s[:3]
'123'
>>> s[:-3]
'123456'
>>>
I think that commit removed a very useful functionality that is no longer achievable with the current version of Jinja (due to an explicit assert() that requires a positive truncation length to be provided. I would suggest to remove that assert to give the opportunity to truncate a string on any end using the truncate filter.
galaxy4public
All 9 comments
Your usecase is not what truncate is meant for it's for truncating long strings (usually with "..." at the end). You can simply use {{ 'November'[:3] }} to get the first three chars in Jinja...
ThiefMaster
on 27 Aug 2019
@ThiefMaster, I actually want to get "ember" from "November", "ober" from "October", etc. Not the first three characters. However, thanks for the tip. I appreciate it. In any case, I just submitted a PR that adjust the logic to preserve all the introduced changes but also makes it possible to truncate for either side of the string :)
galaxy4public
on 27 Aug 2019
[3:] then?
ThiefMaster
on 27 Aug 2019
@ThiefMaster, it seems your hint works with literal strings only. I am using Pelican (a static website generator) and my Jinja2 code is something like the following:
{{ article.date|strftime('%B')|truncate(3, True, '') }}
It seems that it is not possible to use the proposed [:3] in this case, this is why I was relying on truncate.
galaxy4public
on 27 Aug 2019
Try adding parentheses: {{ (article.date|strftime('%B'))[:3] }}
ThiefMaster
on 27 Aug 2019
@ThiefMaster, you are a legend! It works this way. Thanks. However, I still believe that my PR #1053 improves the function by introducing abs() around the length parameter. However, now that you provided a workaround my life is happy again :)
galaxy4public
on 27 Aug 2019
Also, regarding the purpose of the truncate function, it seems the common assumption is that there are only LTR languages, but this is not true. There are RTL languages as Farsi, etc, where truncation should be done on the other end :)
galaxy4public
on 10 Oct 2019
I'm not an expert on RTL, but I'm fairly sure that's a UI thing only, the string is still LTR internally.
davidism
on 10 Oct 2019
Closing as I don't think truncating on the left was ever intended. If you need specific string manipulations, write a specific filter, especially for the given example.
davidism
on 5 Nov 2019
Related issues
nalzok
·
5Comments
AMDmi3
·
4Comments
Yannik
·
4Comments
hvnsweeting
·
4Comments
Xion
·
5Comments
Most helpful comment
Try adding parentheses:
{{ (article.date|strftime('%B'))[:3] }}