Speed up blib2to3 tokenization using startswith with a tuple (#4541)

psf · Dec 30, 2024 · fdabd42 · fdabd42
1 parent 9431e98
commit fdabd42
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diff --git a/CHANGES.md b/CHANGES.md
@@ -43,6 +43,7 @@
 ### Performance
 
 <!-- Changes that improve Black's performance. -->
+- Speed up the `is_fstring_start` function in Black's tokenizer (#4541)
 
 ### Output
 

diff --git a/src/blib2to3/pgen2/tokenize.py b/src/blib2to3/pgen2/tokenize.py
@@ -221,7 +221,7 @@ def _combinations(*l: str) -> set[str]:
     | {f"{prefix}'" for prefix in _strprefixes | _fstring_prefixes}
     | {f'{prefix}"' for prefix in _strprefixes | _fstring_prefixes}
 )
-fstring_prefix: Final = (
+fstring_prefix: Final = tuple(
     {f"{prefix}'" for prefix in _fstring_prefixes}
     | {f'{prefix}"' for prefix in _fstring_prefixes}
     | {f"{prefix}'''" for prefix in _fstring_prefixes}
@@ -459,7 +459,7 @@ def untokenize(iterable: Iterable[TokenInfo]) -> str:
 
 
 def is_fstring_start(token: str) -> bool:
-    return builtins.any(token.startswith(prefix) for prefix in fstring_prefix)
+    return token.startswith(fstring_prefix)
 
 
 def _split_fstring_start_and_middle(token: str) -> tuple[str, str]: