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bpo-28029: Make "".replace("", s, n) returning s for any n != 0. #16981

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Merged
serhiy-storchaka merged 1 commit into from
Oct 30, 2019
Merged

bpo-28029: Make "".replace("", s, n) returning s for any n != 0. #16981

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5 changes: 5 additions & 0 deletions Doc/whatsnew/3.9.rst
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Expand Up @@ -99,6 +99,11 @@ Other Language Changes
ignored for empty strings.
(Contributed by Victor Stinner in :issue:`37388`.)

* ``"".replace("", s, n)`` now returns ``s`` instead of an empty string for
all non-zero ``n``. It is now consistent with ``"".replace("", s)``.
There are similar changes for :class:`bytes` and :class:`bytearray` objects.
(Contributed by Serhiy Storchaka in :issue:`28029`.)


New Modules
===========
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1 change: 1 addition & 0 deletions Lib/test/string_tests.py
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Expand Up @@ -505,6 +505,7 @@ def test_replace(self):
EQ("", "", "replace", "A", "")
EQ("", "", "replace", "A", "A")
EQ("", "", "replace", "", "", 100)
EQ("A", "", "replace", "", "A", 100)
EQ("", "", "replace", "", "", sys.maxsize)

# interleave (from=="", 'to' gets inserted everywhere)
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-10-29-09-38-54.bpo-28029.AmRMEF.rst
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@@ -0,0 +1,3 @@
``"".replace("", s, n)`` now returns ``s`` instead of an empty string for
all non-zero ``n``. There are similar changes for :class:`bytes` and
:class:`bytearray` objects.
13 changes: 5 additions & 8 deletions Objects/stringlib/transmogrify.h
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Expand Up @@ -680,9 +680,13 @@ stringlib_replace(PyObject *self,
const char *to_s, Py_ssize_t to_len,
Py_ssize_t maxcount)
{
if (STRINGLIB_LEN(self) < from_len) {
/* nothing to do; return the original bytes */
return return_self(self);
}
if (maxcount < 0) {
maxcount = PY_SSIZE_T_MAX;
} else if (maxcount == 0 || STRINGLIB_LEN(self) == 0) {
} else if (maxcount == 0) {
/* nothing to do; return the original bytes */
return return_self(self);
}
Expand All @@ -699,13 +703,6 @@ stringlib_replace(PyObject *self,
return stringlib_replace_interleave(self, to_s, to_len, maxcount);
}

/* Except for b"".replace(b"", b"A") == b"A" there is no way beyond this */
/* point for an empty self bytes to generate a non-empty bytes */
/* Special case so the remaining code always gets a non-empty bytes */
if (STRINGLIB_LEN(self) == 0) {
return return_self(self);
}

if (to_len == 0) {
/* delete all occurrences of 'from' bytes */
if (from_len == 1) {
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5 changes: 4 additions & 1 deletion Objects/unicodeobject.c
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Expand Up @@ -10572,9 +10572,12 @@ replace(PyObject *self, PyObject *str1,
int mayshrink;
Py_UCS4 maxchar, maxchar_str1, maxchar_str2;

if (slen < len1)
goto nothing;

if (maxcount < 0)
maxcount = PY_SSIZE_T_MAX;
else if (maxcount == 0 || slen == 0)
else if (maxcount == 0)
goto nothing;

if (str1 == str2)
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