Issue 1519638: Now unmatched groups are replaced with empty strings in re.sub()
and re.subn().
diff --git a/Doc/library/re.rst b/Doc/library/re.rst
index edb2486..48e3006 100644
--- a/Doc/library/re.rst
+++ b/Doc/library/re.rst
@@ -701,6 +701,9 @@
.. versionchanged:: 3.1
Added the optional flags argument.
+ .. versionchanged:: 3.5
+ Unmatched groups are replaced with an empty string.
+
.. function:: subn(pattern, repl, string, count=0, flags=0)
@@ -710,6 +713,9 @@
.. versionchanged:: 3.1
Added the optional flags argument.
+ .. versionchanged:: 3.5
+ Unmatched groups are replaced with an empty string.
+
.. function:: escape(string)
@@ -885,6 +891,8 @@
(``\g<1>``, ``\g<name>``) are replaced by the contents of the
corresponding group.
+ .. versionchanged:: 3.5
+ Unmatched groups are replaced with an empty string.
.. method:: match.group([group1, ...])
diff --git a/Doc/whatsnew/3.5.rst b/Doc/whatsnew/3.5.rst
index feca241..319284a 100644
--- a/Doc/whatsnew/3.5.rst
+++ b/Doc/whatsnew/3.5.rst
@@ -223,6 +223,9 @@
* Number of capturing groups in regular expression is no longer limited by 100.
(Contributed by Serhiy Storchaka in :issue:`22437`.)
+* Now unmatched groups are replaced with empty strings in :func:`re.sub`
+ and :func:`re.subn`. (Contributed by Serhiy Storchaka in :issue:`1519638`.)
+
shutil
------
diff --git a/Lib/sre_parse.py b/Lib/sre_parse.py
index b9a1852..063d1b7 100644
--- a/Lib/sre_parse.py
+++ b/Lib/sre_parse.py
@@ -880,14 +880,12 @@
def expand_template(template, match):
g = match.group
- sep = match.string[:0]
+ empty = match.string[:0]
groups, literals = template
literals = literals[:]
try:
for index, group in groups:
- literals[index] = s = g(group)
- if s is None:
- raise error("unmatched group")
+ literals[index] = g(group) or empty
except IndexError:
raise error("invalid group reference")
- return sep.join(literals)
+ return empty.join(literals)
diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index e5ad6cb..0e4fa88 100644
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -225,9 +225,11 @@
self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g<a a>', 'xx')
self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g<>', 'xx')
self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g<1a1>', 'xx')
+ self.assertRaises(re.error, re.sub, '(?P<a>x)', r'\g<2>', 'xx')
+ self.assertRaises(re.error, re.sub, '(?P<a>x)', r'\2', 'xx')
self.assertRaises(IndexError, re.sub, '(?P<a>x)', '\g<ab>', 'xx')
- self.assertRaises(re.error, re.sub, '(?P<a>x)|(?P<b>y)', '\g<b>', 'xx')
- self.assertRaises(re.error, re.sub, '(?P<a>x)|(?P<b>y)', '\\2', 'xx')
+ self.assertEqual(re.sub('(?P<a>x)|(?P<b>y)', r'\g<b>', 'xx'), '')
+ self.assertEqual(re.sub('(?P<a>x)|(?P<b>y)', r'\2', 'xx'), '')
self.assertRaises(re.error, re.sub, '(?P<a>x)', '\g<-1>', 'xx')
# New valid/invalid identifiers in Python 3
self.assertEqual(re.sub('(?P<µ>x)', r'\g<µ>', 'xx'), 'xx')
@@ -439,6 +441,10 @@
"first second")
.expand(r"\2 \1 \g<second> \g<first>"),
"second first second first")
+ self.assertEqual(re.match("(?P<first>first)|(?P<second>second)",
+ "first")
+ .expand(r"\2 \g<second>"),
+ " ")
def test_repeat_minmax(self):
self.assertIsNone(re.match("^(\w){1}$", "abc"))
diff --git a/Misc/NEWS b/Misc/NEWS
index 21ee7b2..c3932d7 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -166,7 +166,10 @@
Library
-------
-- Issue $18615: sndhdr.what/whathdr now return a namedtuple.
+- Issue 1519638: Now unmatched groups are replaced with empty strings in re.sub()
+ and re.subn().
+
+- Issue #18615: sndhdr.what/whathdr now return a namedtuple.
- Issue #22462: Fix pyexpat's creation of a dummy frame to make it
appear in exception tracebacks.