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Avoid repeated format of union members #22297

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hauntsaninja merged 1 commit into from
Oct 25, 2026
+9 −2
Merged

Avoid repeated format of union members #22297

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11 changes: 9 additions & 2 deletions mypy/messages.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2678,15 +2678,22 @@ def format_list(types: Sequence[Type]) -> str:
return ", ".join(format(typ) for typ in types)

def format_union_items(types: Sequence[Type]) -> list[str]:
formatted = [format(typ) for typ in types if format(typ) != "None"]
formatted = []
has_none = False
for typ in types:
item = format(typ)
if item == "None":
has_none = True
else:
formatted.append(item)
if len(formatted) > MAX_UNION_ITEMS and verbosity == 0:
more = len(formatted) - MAX_UNION_ITEMS // 2
formatted = formatted[: MAX_UNION_ITEMS // 2]
else:
more = 0
if more:
formatted.append(f"<{more} more items>")
if any(format(typ) == "None" for typ in types):
if has_none:
formatted.append("None")
return formatted

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