Django Rusty Templates
Since September 2024, I have been building a reimplementation of Django’s templating language in Rust, called Django Rusty Templates. During this process, I have discovered several weird edge-cases and bugs, some of which I’ve talked about before.
Centring strings
Django supports a template filter for centring strings: {{ "Django"|center:10 }} which adds padding around the string to reach the provided length. In this simple case, the template is rendered as ··Django·· (where · represents a space character).
Things get weird when the total amount of padding required is an odd number. For example, {{ "odd"|center:6 }} becomes ·odd··, but {{ "even"|center:7 }} becomes ··even·. Note that the side with the extra space character is inconsistent.
The cause of this quirk is that Django’s center filter directly calls Python’s str.center method, which maintains this behaviour for backwards compatibilty reasons.
It is possible to get more intuitive behaviour by using f-strings (or older format strings) with the ^ alignment option, which centres the string:
>>> f"{'odd':^6}"
'·odd··'
>>> f"{'even':^7}"
'·even··'
But this isn’t available in the Django template language without defining a custom filter or moving the centring logic out of the template.
Thanks to Moshe Nahmias for working on implementing the center filter in Django Rusty Templates, and finding this quirk.