Custom max and min filters for Jinja2 templates accept an iterable object

[Jun Omae]

Trac core provides custom max and min filters, however the same filters have been added in Jinja2 3.0. The max and min filters in Trac don't accept an iterable object but the same filters in Jinja2 accept an iterable object.

I just encountered this error, I spent 2 days.

>>> tmpl = chrome.jenv.from_string('${ data|map("upper")|max(default="?") }')
>>> tmpl.render(data=['Aaa', 'Bbb', 'ccc'])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/jun66j5/venv/py311/lib/python3.11/site-packages/jinja2/environment.py", line 1304, in render
    self.environment.handle_exception()
  File "/home/jun66j5/venv/py311/lib/python3.11/site-packages/jinja2/environment.py", line 939, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "<template>", line 1, in top-level template code
  File "/home/jun66j5/venv/trac/1.6/lib/python3.11/site-packages/trac/util/presentation.py", line 141, in max_filter
    if len(seq):
       ^^^^^^^^
TypeError: object of type 'generator' has no len()

>>> from jinja2 import Environment, BaseLoader
>>> jenv = Environment(loader=BaseLoader())
>>> tmpl = jenv.from_string('{{ data|map("upper")|max }}')
>>> tmpl.render(data=['Aaa', 'Bbb', 'ccc'])
'CCC'

Work around is to apply list filter before max.

-${ data|map("upper")|max(default="?") }
+${ data|map("upper")|list|max(default="?") }

Patch:

trac/util/presentation.py

@@ -138 +138 @@
 
 def max_filter(seq, default=None):
     """Returns the max value from the sequence."""
-    if len(seq):
-        return max(seq)
-    return default
+    return max(seq, default=default)
 
 def min_filter(seq, default=None):
     """Returns the min value from the sequence."""
-    if len(seq):
-        return min(seq)
-    return default
+    return min(seq, default=default)
 
 
 def trim_filter(value, what=None):

[Jun Omae]

I noticed the min filter is never used due to a typo….

trac/util/presentation.py

@@ -50 +50 @@
         groupattr=groupattr_filter,
         htmlattr=htmlattr_filter,
         max=max_filter,
-        mix=min_filter,
+        min=min_filter,
         trim=trim_filter,
     )
     jenv.tests.update(

[Jun Omae]

Fixed in [17849] and merged in [17852].