Jinja: Incorrect behavior of truncate filter

Created on 3 Apr 2017 · 4Comments · Source: pallets/jinja

Code:

from jinja2 import Template

print(Template('{{ "2016.10.26_cc37528" | truncate(11, True) }}').render())
print(Template('{{ "2016.10.26_cc37528" | truncate(12, True) }}').render())
print(Template('{{ "2016.10.26_cc37528" | truncate(13, True) }}').render())
print(Template('{{ "2016.10.26_cc37528" | truncate(14, True) }}').render())

Expected Behavior

2016.10....
2016.10.2...
2016.10.26...
2016.10.26_...

Actual Behavior

2016.10....
2016.10.2...
2016.10.26_cc37528
2016.10.26_cc37528

Template Code

{{ "2016.10.26_cc37528" | truncate(13, True) }}

Your Environment

Python version: 3.6.1
Jinja version: 2.9.5

Source

AMDmi3

Most helpful comment

It is. Setting leeway to 0 fixes the issue. I'd say it's POLA violation when using short strings.

AMDmi3 on 3 Apr 2017

👍3

All 4 comments

Check whether this is caused by the leeway argument. The default value for it changed recently.

https://github.com/pallets/jinja/blob/master/jinja2/filters.py#L467

ThiefMaster on 3 Apr 2017

It is. Setting leeway to 0 fixes the issue. I'd say it's POLA violation when using short strings.

AMDmi3 on 3 Apr 2017

👍3

Yeah I agree @AMDmi3 . We just hit this issue as well.

The problem is that Jinja has an opinionated implementation which is incompatible with usage as a general purpose templating engine.

macropin on 6 Jul 2017

I also found this problem and spend several hours finding the bug. Clearly new options should be backwards compatible and the default should be leeway = 0.
Whoever starts using the new option leeway they will know it exists and will use the value they please. Those who dont know about the new parameter wont need to change their code...