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fix(filters): do not append fill_with when items divide evenly across slices #2154

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justDance-everybody wants to merge 4 commits into from
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fix(filters): do not append fill_with when items divide evenly across slices #2154

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4c2505b
fix(filters): do not append fill_with when items divide evenly across…
titagass Apr 3, 2026
9e2e474
[pre-commit.ci lite] apply automatic fixes
pre-commit-ci-lite[bot] Apr 3, 2026
38df06c
test(filters): add regression tests for slice filter fill_with behavior
titagass Apr 3, 2026
84cd3a7
[pre-commit.ci lite] apply automatic fixes
pre-commit-ci-lite[bot] Apr 3, 2026
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6 changes: 5 additions & 1 deletion src/jinja2/filters.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1089,7 +1089,11 @@ def sync_do_slice(
end = offset + (slice_number + 1) * items_per_slice
tmp = seq[start:end]

if fill_with is not None and slice_number >= slices_with_extra:
if (
fill_with is not None
Comment on lines +1092 to +1093

Copilot AI Apr 3, 2026

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Please add a regression test for the case where the input length divides evenly by the number of slices (so slices_with_extra == 0). With fill_with provided, this should not append any filler items (e.g., range(9)|slice(3, 'X') should yield [[0,1,2],[3,4,5],[6,7,8]]). This will ensure the bug fixed here doesn’t reappear, and should be covered in both sync and async filter tests if applicable.

Copilot uses AI. Check for mistakes.
and slices_with_extra > 0
and slice_number >= slices_with_extra
):
tmp.append(fill_with)

yield tmp
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13 changes: 13 additions & 0 deletions tests/test_filters.py
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Original file line number Diff line number Diff line change
Expand Up @@ -881,3 +881,16 @@ def test_filter_undefined_in_condexpr(self, env):

with pytest.raises(TemplateRuntimeError, match="No filter named 'f'"):
t2.render(x=42)

def test_slice_no_fill_with_even_division(self, env):
"""fill_with must not be appended when items divide evenly."""
t = env.from_string("{{ items|slice(4, 'X')|list }}")
assert t.render(items=[1, 2, 3, 4]) == "[[1], [2], [3], [4]]"
assert t.render(items=list(range(9))) == ("[[0, 1, 2], [3, 4, 5], [6, 7, 8]]")

def test_slice_fill_with_remainder(self, env):
"""fill_with should only be appended to shorter slices."""
t = env.from_string("{{ items|slice(3, 'X')|list }}")
assert t.render(items=list(range(10))) == (
"[[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 'X']]"
)
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