bpo-29995: re.escape() now escapes only special characters.

Doc/library/re.rst

@@ -786,7 +786,7 @@ form.
 
 .. function:: escape(pattern)
 
-   Escape all the characters in *pattern* except ASCII letters, numbers and ``'_'``.
+   Escape special characters in *pattern*.
    This is useful if you want to match an arbitrary literal string that may
    have regular expression metacharacters in it.  For example::
 
@@ -795,15 +795,19 @@ form.
 
       >>> legal_chars = string.ascii_lowercase + string.digits + "!#$%&'*+-.^_`|~:"
       >>> print('[%s]+' % re.escape(legal_chars))
-      [abcdefghijklmnopqrstuvwxyz0123456789\!\#\$\%\&\'\*\+\-\.\^_\`\|\~\:]+
+      [abcdefghijklmnopqrstuvwxyz0123456789!\#\$%&'\*\+\-\.\^_`\|~:]+
 
       >>> operators = ['+', '-', '*', '/', '**']
       >>> print('|'.join(map(re.escape, sorted(operators, reverse=True))))
-      \/|\-|\+|\*\*|\*
+      /|\-|\+|\*\*|\*
 
    .. versionchanged:: 3.3
       The ``'_'`` character is no longer escaped.
 
+   .. versionchanged:: 3.7
+      Only characters that can have special meaning in a regular expression
+      are escaped.
+
 
 .. function:: purge()
 

Doc/tools/susp-ignored.csv

@@ -303,7 +303,7 @@ whatsnew/3.2,,:gz,">>> with tarfile.open(name='myarchive.tar.gz', mode='w:gz') a
 whatsnew/3.2,,:location,zope9-location = ${zope9:location}
 whatsnew/3.2,,:prefix,zope-conf = ${custom:prefix}/etc/zope.conf
 library/re,,`,!#$%&'*+-.^_`|~:
-library/re,,`,\!\#\$\%\&\'\*\+\-\.\^_\`\|\~\:
+library/re,,`,!\#\$%&'\*\+\-\.\^_`\|~:
 library/tarfile,,:xz,'x:xz'
 library/xml.etree.elementtree,,:sometag,prefix:sometag
 library/xml.etree.elementtree,,:fictional,"<actors xmlns:fictional=""http://characters.example.com"""

Lib/idlelib/idle_test/test_replace.py

@@ -221,8 +221,8 @@ def test_replace_regex(self):
         self.assertIn('Invalid Replace Expression', showerror.message)
 
         # test access method
-        self.engine.setcookedpat("\'")
-        equal(pv.get(), "\\'")
+        self.engine.setcookedpat("?")
+        equal(pv.get(), "\\?")
 
     def test_replace_backwards(self):
         equal = self.assertEqual

Lib/re.py

@@ -241,39 +241,21 @@ def template(pattern, flags=0):
     "Compile a template pattern, returning a pattern object"
     return _compile(pattern, flags|T)
 
-_alphanum_str = frozenset(
-    "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890")
-_alphanum_bytes = frozenset(
-    b"_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890")
+# SPECIAL_CHARS
+# closing ')', '}' and ']'
+# '-' (a range in character set)
+# '#' (comment) and WHITESPACE (ignored) in verbose mode
+_special_chars_map = {i: '\\' + chr(i) for i in b'()[]{}?*+-|^$\\.# \t\n\r\v\f'}
 
 def escape(pattern):
     """
-    Escape all the characters in pattern except ASCII letters, numbers and '_'.
+    Escape special characters in a string.
     """
     if isinstance(pattern, str):
-        alphanum = _alphanum_str
-        s = list(pattern)
-        for i, c in enumerate(pattern):
-            if c not in alphanum:
-                if c == "\000":
-                    s[i] = "\\000"
-                else:
-                    s[i] = "\\" + c
-        return "".join(s)
+        return pattern.translate(_special_chars_map)
     else:
-        alphanum = _alphanum_bytes
-        s = []
-        esc = ord(b"\\")
-        for c in pattern:
-            if c in alphanum:
-                s.append(c)
-            else:
-                if c == 0:
-                    s.extend(b"\\000")
-                else:
-                    s.append(esc)
-                    s.append(c)
-        return bytes(s)
+        pattern = str(pattern, 'latin1')
+        return pattern.translate(_special_chars_map).encode('latin1')
 
 # --------------------------------------------------------------------
 # internals

Lib/test/test_re.py

@@ -904,7 +904,7 @@ def test_search_coverage(self):
         self.assertEqual(re.search(r"a\s", "a ").group(0), "a ")
 
     def assertMatch(self, pattern, text, match=None, span=None,
-                    matcher=re.match):
+                    matcher=re.fullmatch):
         if match is None and span is None:
             # the pattern matches the whole text
             match = text
@@ -917,45 +917,46 @@ def assertMatch(self, pattern, text, match=None, span=None,
         self.assertEqual(m.group(), match)
         self.assertEqual(m.span(), span)
 
+    LITERAL_CHARS = string.ascii_letters + string.digits + '!"%&\',/:;<=>@_`~'
+
     def test_re_escape(self):
-        alnum_chars = string.ascii_letters + string.digits + '_'
         p = ''.join(chr(i) for i in range(256))
         for c in p:
-            if c in alnum_chars:
-                self.assertEqual(re.escape(c), c)
-            elif c == '\x00':
-                self.assertEqual(re.escape(c), '\\000')
-            else:
-                self.assertEqual(re.escape(c), '\\' + c)
             self.assertMatch(re.escape(c), c)
+            self.assertMatch('[' + re.escape(c) + ']', c)
+            self.assertMatch('(?x)' + re.escape(c), c)
         self.assertMatch(re.escape(p), p)
+        for c in '-.]{}':
+            self.assertEqual(re.escape(c)[:1], '\\')
+        literal_chars = self.LITERAL_CHARS
+        self.assertEqual(re.escape(literal_chars), literal_chars)
 
-    def test_re_escape_byte(self):
-        alnum_chars = (string.ascii_letters + string.digits + '_').encode('ascii')
+    def test_re_escape_bytes(self):
         p = bytes(range(256))
         for i in p:
             b = bytes([i])
-            if b in alnum_chars:
-                self.assertEqual(re.escape(b), b)
-            elif i == 0:
-                self.assertEqual(re.escape(b), b'\\000')
-            else:
-                self.assertEqual(re.escape(b), b'\\' + b)
             self.assertMatch(re.escape(b), b)
+            self.assertMatch(b'[' + re.escape(b) + b']', b)
+            self.assertMatch(b'(?x)' + re.escape(b), b)
         self.assertMatch(re.escape(p), p)
+        for i in b'-.]{}':
+            b = bytes([i])
+            self.assertEqual(re.escape(b)[:1], b'\\')
+        literal_chars = self.LITERAL_CHARS.encode('ascii')
+        self.assertEqual(re.escape(literal_chars), literal_chars)
 
     def test_re_escape_non_ascii(self):
         s = 'xxx\u2620\u2620\u2620xxx'
         s_escaped = re.escape(s)
-        self.assertEqual(s_escaped, 'xxx\\\u2620\\\u2620\\\u2620xxx')
+        self.assertEqual(s_escaped, s)
         self.assertMatch(s_escaped, s)
         self.assertMatch('.%s+.' % re.escape('\u2620'), s,
                          'x\u2620\u2620\u2620x', (2, 7), re.search)
 
     def test_re_escape_non_ascii_bytes(self):
         b = 'y\u2620y\u2620y'.encode('utf-8')
         b_escaped = re.escape(b)
-        self.assertEqual(b_escaped, b'y\\\xe2\\\x98\\\xa0y\\\xe2\\\x98\\\xa0y')
+        self.assertEqual(b_escaped, b)
         self.assertMatch(b_escaped, b)
         res = re.findall(re.escape('\u2620'.encode('utf-8')), b)
         self.assertEqual(len(res), 2)

Misc/NEWS

@@ -320,6 +320,8 @@ Library
 - bpo-29998: Pickling and copying ImportError now preserves name and path
   attributes.
 
+- bpo-29995: re.escape() now escapes only regex special characters.
+
 - bpo-29962: Add math.remainder operation, implementing remainder
   as specified in IEEE 754.