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gh-153568: Skip newline translation for source without carriage returns #153584

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gh-153568: Skip newline translation for source without carriage returns #153584

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2 changes: 2 additions & 0 deletions .../NEWS.d/next/Core_and_Builtins/2026-07-11-16-53-21.gh-issue-153568.newlines.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Speed up the tokenizer by copying source text verbatim when it contains no
carriage returns.
11 changes: 10 additions & 1 deletion Parser/tokenizer/helpers.c
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Original file line number Diff line number Diff line change
Expand Up @@ -265,7 +265,8 @@ char *
_PyTokenizer_translate_newlines(const char *s, int exec_input, int preserve_crlf,
struct tok_state *tok) {
int skip_next_lf = 0;
size_t needed_length = strlen(s) + 2, final_length;
size_t input_length = strlen(s);
size_t needed_length = input_length + 2, final_length;
char *buf, *current;
char c = '\0';
buf = PyMem_Malloc(needed_length);
Expand All @@ -274,6 +275,13 @@ _PyTokenizer_translate_newlines(const char *s, int exec_input, int preserve_crlf
PyErr_NoMemory();
return NULL;
}
if (memchr(s, '\r', input_length) == NULL) {
// No carriage returns: nothing to translate, copy verbatim.
memcpy(buf, s, input_length);
current = buf + input_length;
c = input_length ? s[input_length - 1] : '\0';
goto add_final_newline;
Comment on lines +282 to +283

@maurycy maurycy Jul 11, 2026 •
edited
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Suggested change
c = input_length ? s[input_length - 1] : '\0';
goto add_final_newline;
if (exec_input && input_length && s[input_length - 1] != '\n') {
*current++ = '\n';
}
*current = '\0';
return buf;

Do you think it makes sense to spare PyMem_Realloc()?

}
for (current = buf; *s; s++, current++) {
c = *s;
if (skip_next_lf) {
Expand All @@ -290,6 +298,7 @@ _PyTokenizer_translate_newlines(const char *s, int exec_input, int preserve_crlf
}
*current = c;
}
add_final_newline:
/* If this is exec input, add a newline to the end of the string if
there isn't one already. */
if (exec_input && c != '\n' && c != '\0') {
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