bpo-29995: re.escape() now escapes only special characters. (#1007)

diff --git a/Lib/idlelib/idle_test/test_replace.py b/Lib/idlelib/idle_test/test_replace.py
index 9913ed2..2ecbd34 100644
--- a/Lib/idlelib/idle_test/test_replace.py
+++ b/Lib/idlelib/idle_test/test_replace.py
@@ -221,8 +221,8 @@
         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
diff --git a/Lib/re.py b/Lib/re.py
index d321cff..7053edd 100644
--- a/Lib/re.py
+++ b/Lib/re.py
@@ -241,39 +241,21 @@
     "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
diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index a1fddfb..b3b29f8 100644
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -904,7 +904,7 @@
         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
@@ -917,37 +917,38 @@
         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)
@@ -955,7 +956,7 @@
     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)