#2834: Change re module semantics, so that str and bytes mixing is forbidden,

and str (unicode) patterns get full unicode matching by default. The re.ASCII
flag is also introduced to ask for ASCII matching instead.

37 files changed, 280 insertions, 163 deletions

diff --git a/Doc/library/re.rst b/Doc/library/re.rst
index a6ebc22..f6f0d89 100644
--- a/Doc/library/re.rst
+++ b/Doc/library/re.rst
@@ -11,9 +11,13 @@
 
 
 This module provides regular expression matching operations similar to
-those found in Perl. Both patterns and strings to be searched can be
-Unicode strings as well as 8-bit strings.  The :mod:`re` module is
-always available.
+those found in Perl.  The :mod:`re` module is always available.
+
+Both patterns and strings to be searched can be Unicode strings as well as
+8-bit strings. However, Unicode strings and 8-bit strings cannot be mixed:
+that is, you cannot match an Unicode string with a byte pattern or
+vice-versa; similarly, when asking for a substition, the replacement
+string must be of the same type as both the pattern and the search string.
 
 Regular expressions use the backslash character (``'\'``) to indicate
 special forms or to allow special characters to be used without invoking
@@ -212,12 +216,12 @@ The special characters are:
    group; ``(?P<name>...)`` is the only exception to this rule. Following are the
    currently supported extensions.
 
-``(?iLmsux)``
-   (One or more letters from the set ``'i'``, ``'L'``, ``'m'``, ``'s'``,
-   ``'u'``, ``'x'``.)  The group matches the empty string; the letters
-   set the corresponding flags: :const:`re.I` (ignore case),
-   :const:`re.L` (locale dependent), :const:`re.M` (multi-line),
-   :const:`re.S` (dot matches all), :const:`re.U` (Unicode dependent),
+``(?aiLmsux)``
+   (One or more letters from the set ``'a'``, ``'i'``, ``'L'``, ``'m'``,
+   ``'s'``, ``'u'``, ``'x'``.)  The group matches the empty string; the
+   letters set the corresponding flags: :const:`re.a` (ASCII-only matching),
+   :const:`re.I` (ignore case), :const:`re.L` (locale dependent),
+   :const:`re.M` (multi-line), :const:`re.S` (dot matches all), 
    and :const:`re.X` (verbose), for the entire regular expression. (The
    flags are described in :ref:`contents-of-module-re`.) This
    is useful if you wish to include the flags as part of the regular
@@ -324,56 +328,62 @@ the second character.  For example, ``\$`` matches the character ``'$'``.
    word is indicated by whitespace or a non-alphanumeric, non-underscore character.
    Note that  ``\b`` is defined as the boundary between ``\w`` and ``\ W``, so the
    precise set of characters deemed to be alphanumeric depends on the values of the
-   ``UNICODE`` and ``LOCALE`` flags.  Inside a character range, ``\b`` represents
+   ``ASCII`` and ``LOCALE`` flags.  Inside a character range, ``\b`` represents
    the backspace character, for compatibility with Python's string literals.
 
 ``\B``
    Matches the empty string, but only when it is *not* at the beginning or end of a
    word.  This is just the opposite of ``\b``, so is also subject to the settings
-   of ``LOCALE`` and ``UNICODE``.
+   of ``ASCII`` and ``LOCALE`` .
 
 ``\d``
-   When the :const:`UNICODE` flag is not specified, matches any decimal digit; this
-   is equivalent to the set ``[0-9]``.  With :const:`UNICODE`, it will match
-   whatever is classified as a digit in the Unicode character properties database.
+   For Unicode (str) patterns:
+      When the :const:`ASCII` flag is specified, matches any decimal digit; this
+      is equivalent to the set ``[0-9]``.  Otherwise, it will match whatever
+      is classified as a digit in the Unicode character properties database
+      (but this does include the standard ASCII digits and is thus a superset
+      of [0-9]).
+   For 8-bit (bytes) patterns:
+      Matches any decimal digit; this is equivalent to the set ``[0-9]``.
 
 ``\D``
-   When the :const:`UNICODE` flag is not specified, matches any non-digit
-   character; this is equivalent to the set  ``[^0-9]``.  With :const:`UNICODE`, it
-   will match  anything other than character marked as digits in the Unicode
-   character  properties database.
+   Matches any character which is not a decimal digit. This is the
+   opposite of ``\d`` and is therefore similarly subject to the settings of
+   ``ASCII`` and ``LOCALE``.
 
 ``\s``
-   When the :const:`LOCALE` and :const:`UNICODE` flags are not specified, matches
-   any whitespace character; this is equivalent to the set ``[ \t\n\r\f\v]``. With
-   :const:`LOCALE`, it will match this set plus whatever characters are defined as
-   space for the current locale. If :const:`UNICODE` is set, this will match the
-   characters ``[ \t\n\r\f\v]`` plus whatever is classified as space in the Unicode
-   character properties database.
+   For Unicode (str) patterns:
+      When the :const:`ASCII` flag is specified, matches only ASCII whitespace
+      characters; this is equivalent to the set ``[ \t\n\r\f\v]``. Otherwise,
+      it will match this set whatever is classified as space in the Unicode
+      character properties database (including for example the non-breaking
+      spaces mandated by typography rules in many languages).
+   For 8-bit (bytes) patterns:
+      Matches characters considered whitespace in the ASCII character set;
+      this is equivalent to the set ``[ \t\n\r\f\v]``.
 
 ``\S``
-   When the :const:`LOCALE` and :const:`UNICODE` flags are not specified, matches
-   any non-whitespace character; this is equivalent to the set ``[^ \t\n\r\f\v]``
-   With :const:`LOCALE`, it will match any character not in this set, and not
-   defined as space in the current locale. If :const:`UNICODE` is set, this will
-   match anything other than ``[ \t\n\r\f\v]`` and characters marked as space in
-   the Unicode character properties database.
+   Matches any character which is not a whitespace character. This is the
+   opposite of ``\s`` and is therefore similarly subject to the settings of
+   ``ASCII`` and ``LOCALE``.
 
 ``\w``
-   When the :const:`LOCALE` and :const:`UNICODE` flags are not specified, matches
-   any alphanumeric character and the underscore; this is equivalent to the set
-   ``[a-zA-Z0-9_]``.  With :const:`LOCALE`, it will match the set ``[0-9_]`` plus
-   whatever characters are defined as alphanumeric for the current locale.  If
-   :const:`UNICODE` is set, this will match the characters ``[0-9_]`` plus whatever
-   is classified as alphanumeric in the Unicode character properties database.
+   For Unicode (str) patterns:
+      When the :const:`ASCII` flag is specified, this is equivalent to the set
+      ``[a-zA-Z0-9_]``. Otherwise, it will match whatever is classified as
+      alphanumeric in the Unicode character properties database (it will
+      include most characters that can be part of a word in whatever language,
+      as well as numbers and the underscore sign).
+   For 8-bit (bytes) patterns:
+      Matches characters considered alphanumeric in the ASCII character set;
+      this is equivalent to the set ``[a-zA-Z0-9_]``. With :const:`LOCALE`, 
+      it will additionally match whatever characters are defined as
+      alphanumeric for the current locale.
 
 ``\W``
-   When the :const:`LOCALE` and :const:`UNICODE` flags are not specified, matches
-   any non-alphanumeric character; this is equivalent to the set ``[^a-zA-Z0-9_]``.
-   With :const:`LOCALE`, it will match any character not in the set ``[0-9_]``, and
-   not defined as alphanumeric for the current locale. If :const:`UNICODE` is set,
-   this will match anything other than ``[0-9_]`` and characters marked as
-   alphanumeric in the Unicode character properties database.
+   Matches any character which is not an alphanumeric character. This is the
+   opposite of ``\w`` and is therefore similarly subject to the settings of
+   ``ASCII`` and ``LOCALE``.
 
 ``\Z``
    Matches only at the end of the string.
@@ -454,6 +464,25 @@ form.
       expression at a time needn't worry about compiling regular expressions.)
 
 
+.. data:: A
+          ASCII
+
+   Make ``\w``, ``\W``, ``\b``, ``\B``, ``\s`` and ``\S`` perform ASCII-only
+   matching instead of full Unicode matching. This is only meaningful for
+   Unicode patterns, and is ignored for byte patterns.
+
+   Note that the :const:`re.U` flag still exists (as well as its synonym
+   :const:`re.UNICODE` and its embedded counterpart ``(?u)``), but it has
+   become useless in Python 3.0.
+   In previous Python versions, it was used to specify that 
+   matching had to be Unicode dependent (the default was ASCII matching in
+   all circumstances). Starting from Python 3.0, the default is Unicode 
+   matching for Unicode strings (which can be changed by specifying the
+   ``'a'`` flag), and ASCII matching for 8-bit strings. Further, Unicode
+   dependent matching for 8-bit strings isn't allowed anymore and results
+   in a ValueError.
+
+
 .. data:: I
           IGNORECASE
 
@@ -465,7 +494,10 @@ form.
           LOCALE
 
    Make ``\w``, ``\W``, ``\b``, ``\B``, ``\s`` and ``\S`` dependent on the
-   current locale.
+   current locale. The use of this flag is discouraged as the locale mechanism
+   is very unreliable, and it only handles one "culture" at a time anyway;
+   you should use Unicode matching instead, which is the default in Python 3.0
+   for Unicode (str) patterns.
 
 
 .. data:: M
@@ -486,13 +518,6 @@ form.
    newline; without this flag, ``'.'`` will match anything *except* a newline.
 
 
-.. data:: U
-          UNICODE
-
-   Make ``\w``, ``\W``, ``\b``, ``\B``, ``\d``, ``\D``, ``\s`` and ``\S`` dependent
-   on the Unicode character properties database.
-
-
 .. data:: X
           VERBOSE
 
@@ -511,6 +536,8 @@ form.
       b = re.compile(r"\d+\.\d*")
 
 
+
+
 .. function:: search(pattern, string[, flags])
 
    Scan through *string* looking for a location where the regular expression
diff --git a/Lib/_strptime.py b/Lib/_strptime.py
index c3568b0..896c798 100644
--- a/Lib/_strptime.py
+++ b/Lib/_strptime.py
@@ -14,7 +14,7 @@ import time
 import locale
 import calendar
 from re import compile as re_compile
-from re import IGNORECASE
+from re import IGNORECASE, ASCII
 from re import escape as re_escape
 from datetime import date as datetime_date
 try:
@@ -262,7 +262,7 @@ class TimeRE(dict):
 
     def compile(self, format):
         """Return a compiled re object for the format string."""
-        return re_compile(self.pattern(format), IGNORECASE)
+        return re_compile(self.pattern(format), IGNORECASE | ASCII)
 
 _cache_lock = _thread_allocate_lock()
 # DO NOT modify _TimeRE_cache or _regex_cache without acquiring the cache lock
diff --git a/Lib/base64.py b/Lib/base64.py
index fc80835..4308fb4 100755
--- a/Lib/base64.py
+++ b/Lib/base64.py
@@ -39,7 +39,7 @@ def _translate(s, altchars):
     return s.translate(translation)
 
 
-
+
 # Base64 encoding/decoding uses binascii
 
 def b64encode(s, altchars=None):
@@ -126,7 +126,7 @@ def urlsafe_b64decode(s):
     return b64decode(s, b'-_')
 
 
-
+
 # Base32 encoding/decoding must be done in Python
 _b32alphabet = {
     0: b'A',  9: b'J', 18: b'S', 27: b'3',
@@ -225,7 +225,7 @@ def b32decode(s, casefold=False, map01=None):
     # characters because this will tell us how many null bytes to remove from
     # the end of the decoded string.
     padchars = 0
-    mo = re.search('(?P<pad>[=]*)$', s)
+    mo = re.search(b'(?P<pad>[=]*)$', s)
     if mo:
         padchars = len(mo.group('pad'))
         if padchars > 0:
@@ -262,7 +262,7 @@ def b32decode(s, casefold=False, map01=None):
     return b''.join(parts)
 
 
-
+
 # RFC 3548, Base 16 Alphabet specifies uppercase, but hexlify() returns
 # lowercase.  The RFC also recommends against accepting input case
 # insensitively.
@@ -291,12 +291,12 @@ def b16decode(s, casefold=False):
         raise TypeError("expected bytes, not %s" % s.__class__.__name__)
     if casefold:
         s = s.upper()
-    if re.search('[^0-9A-F]', s):
+    if re.search(b'[^0-9A-F]', s):
         raise binascii.Error('Non-base16 digit found')
     return binascii.unhexlify(s)
 
 
-
+
 # Legacy interface.  This code could be cleaned up since I don't believe
 # binascii has any line length limitations.  It just doesn't seem worth it
 # though.  The files should be opened in binary mode.
@@ -353,7 +353,7 @@ def decodestring(s):
     return binascii.a2b_base64(s)
 
 
-
+
 # Usable as a script...
 def main():
     """Small main program"""
diff --git a/Lib/decimal.py b/Lib/decimal.py
index 2c02f11..88cc5cd 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -5415,7 +5415,7 @@ ExtendedContext = Context(
 # 2. For finite numbers (not infinities and NaNs) the body of the
 # number between the optional sign and the optional exponent must have
 # at least one decimal digit, possibly after the decimal point.  The
-# lookahead expression '(?=\d|\.\d)' checks this.
+# lookahead expression '(?=[0-9]|\.[0-9])' checks this.
 #
 # As the flag UNICODE is not enabled here, we're explicitly avoiding any
 # other meaning for \d than the numbers [0-9].
diff --git a/Lib/distutils/cygwinccompiler.py b/Lib/distutils/cygwinccompiler.py
index 48875230..da2c74a 100644
--- a/Lib/distutils/cygwinccompiler.py
+++ b/Lib/distutils/cygwinccompiler.py
@@ -409,7 +409,7 @@ def get_versions():
         out = os.popen(gcc_exe + ' -dumpversion','r')
         out_string = out.read()
         out.close()
-        result = re.search('(\d+\.\d+(\.\d+)*)',out_string)
+        result = re.search('(\d+\.\d+(\.\d+)*)', out_string, re.ASCII)
         if result:
             gcc_version = StrictVersion(result.group(1))
         else:
@@ -421,7 +421,7 @@ def get_versions():
         out = os.popen(ld_exe + ' -v','r')
         out_string = out.read()
         out.close()
-        result = re.search('(\d+\.\d+(\.\d+)*)',out_string)
+        result = re.search('(\d+\.\d+(\.\d+)*)', out_string, re.ASCII)
         if result:
             ld_version = StrictVersion(result.group(1))
         else:
@@ -433,7 +433,7 @@ def get_versions():
         out = os.popen(dllwrap_exe + ' --version','r')
         out_string = out.read()
         out.close()
-        result = re.search(' (\d+\.\d+(\.\d+)*)',out_string)
+        result = re.search(' (\d+\.\d+(\.\d+)*)', out_string, re.ASCII)
         if result:
             dllwrap_version = StrictVersion(result.group(1))
         else:
diff --git a/Lib/distutils/emxccompiler.py b/Lib/distutils/emxccompiler.py
index d9ee82d..62a4c5b 100644
--- a/Lib/distutils/emxccompiler.py
+++ b/Lib/distutils/emxccompiler.py
@@ -300,7 +300,7 @@ def get_versions():
         out = os.popen(gcc_exe + ' -dumpversion','r')
         out_string = out.read()
         out.close()
-        result = re.search('(\d+\.\d+\.\d+)',out_string)
+        result = re.search('(\d+\.\d+\.\d+)', out_string, re.ASCII)
         if result:
             gcc_version = StrictVersion(result.group(1))
         else:
diff --git a/Lib/distutils/sysconfig.py b/Lib/distutils/sysconfig.py
index 3a120dd..b17743a 100644
--- a/Lib/distutils/sysconfig.py
+++ b/Lib/distutils/sysconfig.py
@@ -512,7 +512,7 @@ def get_config_vars(*args):
                         # patched up as well.
                         'CFLAGS', 'PY_CFLAGS', 'BLDSHARED'):
                     flags = _config_vars[key]
-                    flags = re.sub('-arch\s+\w+\s', ' ', flags)
+                    flags = re.sub('-arch\s+\w+\s', ' ', flags, re.ASCII)
                     flags = re.sub('-isysroot [^ \t]*', ' ', flags)
                     _config_vars[key] = flags
 
diff --git a/Lib/distutils/util.py b/Lib/distutils/util.py
index 76798b9..b87dfbe 100644
--- a/Lib/distutils/util.py
+++ b/Lib/distutils/util.py
@@ -81,7 +81,7 @@ def get_platform ():
         return "%s-%s.%s" % (osname, version, release)
     elif osname[:6] == "cygwin":
         osname = "cygwin"
-        rel_re = re.compile (r'[\d.]+')
+        rel_re = re.compile (r'[\d.]+', re.ASCII)
         m = rel_re.match(release)
         if m:
             release = m.group()
diff --git a/Lib/distutils/version.py b/Lib/distutils/version.py
index f71b2f6..907f71c 100644
--- a/Lib/distutils/version.py
+++ b/Lib/distutils/version.py
@@ -134,7 +134,7 @@ class StrictVersion (Version):
     """
 
     version_re = re.compile(r'^(\d+) \. (\d+) (\. (\d+))? ([ab](\d+))?$',
-                            re.VERBOSE)
+                            re.VERBOSE | re.ASCII)
 
 
     def parse (self, vstring):
diff --git a/Lib/distutils/versionpredicate.py b/Lib/distutils/versionpredicate.py
index 434b34f..b0dd9f4 100644
--- a/Lib/distutils/versionpredicate.py
+++ b/Lib/distutils/versionpredicate.py
@@ -5,7 +5,8 @@ import distutils.version
 import operator
 
 
-re_validPackage = re.compile(r"(?i)^\s*([a-z_]\w*(?:\.[a-z_]\w*)*)(.*)")
+re_validPackage = re.compile(r"(?i)^\s*([a-z_]\w*(?:\.[a-z_]\w*)*)(.*)",
+    re.ASCII)
 # (package) (rest)
 
 re_paren = re.compile(r"^\s*\((.*)\)\s*$") # (list) inside of parentheses
@@ -153,7 +154,8 @@ def split_provision(value):
     global _provision_rx
     if _provision_rx is None:
         _provision_rx = re.compile(
-            "([a-zA-Z_]\w*(?:\.[a-zA-Z_]\w*)*)(?:\s*\(\s*([^)\s]+)\s*\))?$")
+            "([a-zA-Z_]\w*(?:\.[a-zA-Z_]\w*)*)(?:\s*\(\s*([^)\s]+)\s*\))?$",
+            re.ASCII)
     value = value.strip()
     m = _provision_rx.match(value)
     if not m:
diff --git a/Lib/email/quoprimime.py b/Lib/email/quoprimime.py
index 68dc11c..ca91631 100644
--- a/Lib/email/quoprimime.py
+++ b/Lib/email/quoprimime.py
@@ -70,7 +70,7 @@ for c in (b' !"#$%&\'()*+,-./0123456789:;<>'
     _QUOPRI_BODY_MAP[c] = chr(c)
 
 
-
+
 # Helpers
 def header_check(octet):
     """Return True if the octet should be escaped with header quopri."""
@@ -125,7 +125,7 @@ def quote(c):
     return '=%02X' % ord(c)
 
 
-
+
 def header_encode(header_bytes, charset='iso-8859-1'):
     """Encode a single header line with quoted-printable (like) encoding.
 
@@ -149,7 +149,7 @@ def header_encode(header_bytes, charset='iso-8859-1'):
     return '=?%s?q?%s?=' % (charset, EMPTYSTRING.join(encoded))
 
 
-
+
 def body_encode(body, maxlinelen=76, eol=NL):
     """Encode with quoted-printable, wrapping at maxlinelen characters.
 
@@ -225,7 +225,7 @@ def body_encode(body, maxlinelen=76, eol=NL):
     return encoded_body
 
 
-
+
 # BAW: I'm not sure if the intent was for the signature of this function to be
 # the same as base64MIME.decode() or not...
 def decode(encoded, eol=NL):
@@ -280,7 +280,7 @@ body_decode = decode
 decodestring = decode
 
 
-
+
 def _unquote_match(match):
     """Turn a match in the form =AB to the ASCII character with value 0xab"""
     s = match.group(0)
@@ -296,4 +296,4 @@ def header_decode(s):
     the high level email.Header class for that functionality.
     """
     s = s.replace('_', ' ')
-    return re.sub(r'=\w{2}', _unquote_match, s)
+    return re.sub(r'=\w{2}', _unquote_match, s, re.ASCII)
diff --git a/Lib/email/utils.py b/Lib/email/utils.py
index 35275f6..465903f 100644
--- a/Lib/email/utils.py
+++ b/Lib/email/utils.py
@@ -52,7 +52,7 @@ specialsre = re.compile(r'[][\\()<>@,:;".]')
 escapesre = re.compile(r'[][\\()"]')
 
 
-
+
 # Helpers
 
 def formataddr(pair):
@@ -73,7 +73,7 @@ def formataddr(pair):
     return address
 
 
-
+
 def getaddresses(fieldvalues):
     """Return a list of (REALNAME, EMAIL) for each fieldvalue."""
     all = COMMASPACE.join(fieldvalues)
@@ -81,7 +81,7 @@ def getaddresses(fieldvalues):
     return a.addresslist
 
 
-
+
 ecre = re.compile(r'''
   =\?                   # literal =?
   (?P<charset>[^?]*?)   # non-greedy up to the next ? is the charset
@@ -93,7 +93,7 @@ ecre = re.compile(r'''
   ''', re.VERBOSE | re.IGNORECASE)
 
 
-
+
 def formatdate(timeval=None, localtime=False, usegmt=False):
     """Returns a date string as specified by RFC 2822, e.g.:
 
@@ -146,7 +146,7 @@ def formatdate(timeval=None, localtime=False, usegmt=False):
         zone)
 
 
-
+
 def make_msgid(idstring=None):
     """Returns a string suitable for RFC 2822 compliant Message-ID, e.g:
 
@@ -168,7 +168,7 @@ def make_msgid(idstring=None):
     return msgid
 
 
-
+
 # These functions are in the standalone mimelib version only because they've
 # subsequently been fixed in the latest Python versions.  We use this to worm
 # around broken older Pythons.
@@ -202,7 +202,7 @@ def unquote(str):
     return str
 
 
-
+
 # RFC2231-related functions - parameter encoding and decoding
 def decode_rfc2231(s):
     """Decode string according to RFC 2231"""
@@ -227,7 +227,8 @@ def encode_rfc2231(s, charset=None, language=None):
     return "%s'%s'%s" % (charset, language, s)
 
 
-rfc2231_continuation = re.compile(r'^(?P<name>\w+)\*((?P<num>[0-9]+)\*?)?$')
+rfc2231_continuation = re.compile(r'^(?P<name>\w+)\*((?P<num>[0-9]+)\*?)?$',
+    re.ASCII)
 
 def decode_params(params):
     """Decode parameters list according to RFC 2231.
diff --git a/Lib/encodings/idna.py b/Lib/encodings/idna.py
index c2ba1da..583bdf1 100644
--- a/Lib/encodings/idna.py
+++ b/Lib/encodings/idna.py
@@ -176,12 +176,10 @@ class Codec(codecs.Codec):
             return "", 0
 
         # IDNA allows decoding to operate on Unicode strings, too.
-        if isinstance(input, bytes):
-            labels = dots.split(input)
-        else:
-            # Force to bytes
+        if not isinstance(input, bytes):
+            # XXX obviously wrong, see #3232
             input = bytes(input)
-            labels = input.split(b".")
+        labels = input.split(b".")
 
         if labels and len(labels[-1]) == 0:
             trailing_dot = '.'
diff --git a/Lib/ftplib.py b/Lib/ftplib.py
index 4955727..b64e45e 100644
--- a/Lib/ftplib.py
+++ b/Lib/ftplib.py
@@ -590,7 +590,8 @@ def parse150(resp):
     global _150_re
     if _150_re is None:
         import re
-        _150_re = re.compile("150 .* \((\d+) bytes\)", re.IGNORECASE)
+        _150_re = re.compile(
+            "150 .* \((\d+) bytes\)", re.IGNORECASE | re.ASCII)
     m = _150_re.match(resp)
     if not m:
         return None
@@ -613,7 +614,7 @@ def parse227(resp):
     global _227_re
     if _227_re is None:
         import re
-        _227_re = re.compile(r'(\d+),(\d+),(\d+),(\d+),(\d+),(\d+)')
+        _227_re = re.compile(r'(\d+),(\d+),(\d+),(\d+),(\d+),(\d+)', re.ASCII)
     m = _227_re.search(resp)
     if not m:
         raise error_proto(resp)
diff --git a/Lib/html/parser.py b/Lib/html/parser.py
index 828eece..83a5825 100644
--- a/Lib/html/parser.py
+++ b/Lib/html/parser.py
@@ -385,4 +385,4 @@ class HTMLParser(_markupbase.ParserBase):
                     return '&'+s+';'
 
         return re.sub(r"&(#?[xX]?(?:[0-9a-fA-F]+|\w{1,8}));",
-                      replaceEntities, s)
+                      replaceEntities, s, re.ASCII)
diff --git a/Lib/http/cookiejar.py b/Lib/http/cookiejar.py
index afd5f20..e9efab8 100644
--- a/Lib/http/cookiejar.py
+++ b/Lib/http/cookiejar.py
@@ -121,7 +121,7 @@ def time2netscape(t=None):
 
 UTC_ZONES = {"GMT": None, "UTC": None, "UT": None, "Z": None}
 
-TIMEZONE_RE = re.compile(r"^([-+])?(\d\d?):?(\d\d)?$")
+TIMEZONE_RE = re.compile(r"^([-+])?(\d\d?):?(\d\d)?$", re.ASCII)
 def offset_from_tz_string(tz):
     offset = None
     if tz in UTC_ZONES:
@@ -191,9 +191,9 @@ def _str2time(day, mon, yr, hr, min, sec, tz):
 
 STRICT_DATE_RE = re.compile(
     r"^[SMTWF][a-z][a-z], (\d\d) ([JFMASOND][a-z][a-z]) "
-    "(\d\d\d\d) (\d\d):(\d\d):(\d\d) GMT$")
+    "(\d\d\d\d) (\d\d):(\d\d):(\d\d) GMT$", re.ASCII)
 WEEKDAY_RE = re.compile(
-    r"^(?:Sun|Mon|Tue|Wed|Thu|Fri|Sat)[a-z]*,?\s*", re.I)
+    r"^(?:Sun|Mon|Tue|Wed|Thu|Fri|Sat)[a-z]*,?\s*", re.I | re.ASCII)
 LOOSE_HTTP_DATE_RE = re.compile(
     r"""^
     (\d\d?)            # day
@@ -210,7 +210,7 @@ LOOSE_HTTP_DATE_RE = re.compile(
     ([-+]?\d{2,4}|(?![APap][Mm]\b)[A-Za-z]+)? # timezone
        \s*
     (?:\(\w+\))?       # ASCII representation of timezone in parens.
-       \s*$""", re.X)
+       \s*$""", re.X | re.ASCII)
 def http2time(text):
     """Returns time in seconds since epoch of time represented by a string.
 
@@ -282,7 +282,7 @@ ISO_DATE_RE = re.compile(
       \s*
    ([-+]?\d\d?:?(:?\d\d)?
     |Z|z)?               # timezone  (Z is "zero meridian", i.e. GMT)
-      \s*$""", re.X)
+      \s*$""", re.X | re. ASCII)
 def iso2time(text):
     """
     As for http2time, but parses the ISO 8601 formats:
@@ -489,7 +489,7 @@ def parse_ns_headers(ns_headers):
     return result
 
 
-IPV4_RE = re.compile(r"\.\d+$")
+IPV4_RE = re.compile(r"\.\d+$", re.ASCII)
 def is_HDN(text):
     """Return True if text is a host domain name."""
     # XXX
@@ -574,7 +574,7 @@ def user_domain_match(A, B):
         return True
     return False
 
-cut_port_re = re.compile(r":\d+$")
+cut_port_re = re.compile(r":\d+$", re.ASCII)
 def request_host(request):
     """Return request-host, as defined by RFC 2965.
 
@@ -1207,7 +1207,7 @@ class CookieJar:
     domain_re = re.compile(r"[^.]*")
     dots_re = re.compile(r"^\.+")
 
-    magic_re = r"^\#LWP-Cookies-(\d+\.\d+)"
+    magic_re = re.compile(r"^\#LWP-Cookies-(\d+\.\d+)", re.ASCII)
 
     def __init__(self, policy=None):
         if policy is None:
@@ -1856,7 +1856,7 @@ class LWPCookieJar(FileCookieJar):
 
     def _really_load(self, f, filename, ignore_discard, ignore_expires):
         magic = f.readline()
-        if not re.search(self.magic_re, magic):
+        if not self.magic_re.search(magic):
             msg = ("%r does not look like a Set-Cookie3 (LWP) format "
                    "file" % filename)
             raise LoadError(msg)
@@ -1965,7 +1965,7 @@ class MozillaCookieJar(FileCookieJar):
     header by default (Mozilla can cope with that).
 
     """
-    magic_re = "#( Netscape)? HTTP Cookie File"
+    magic_re = re.compile("#( Netscape)? HTTP Cookie File")
     header = """\
     # Netscape HTTP Cookie File
     # http://www.netscape.com/newsref/std/cookie_spec.html
@@ -1977,7 +1977,7 @@ class MozillaCookieJar(FileCookieJar):
         now = time.time()
 
         magic = f.readline()
-        if not re.search(self.magic_re, magic):
+        if not self.magic_re.search(magic):
             f.close()
             raise LoadError(
                 "%r does not look like a Netscape format cookies file" %
diff --git a/Lib/http/cookies.py b/Lib/http/cookies.py
index 344bede..3242d83 100644
--- a/Lib/http/cookies.py
+++ b/Lib/http/cookies.py
@@ -445,7 +445,7 @@ _CookiePattern = re.compile(
     ""+ _LegalCharsPatt +"*"        # Any word or empty string
     r")"                          # End of group 'val'
     r"\s*;?"                      # Probably ending in a semi-colon
-    )
+    , re.ASCII)                   # May be removed if safe.
 
 
 # At long last, here is the cookie class.
diff --git a/Lib/imaplib.py b/Lib/imaplib.py
index 0d9704e..156b15d 100644
--- a/Lib/imaplib.py
+++ b/Lib/imaplib.py
@@ -88,11 +88,12 @@ InternalDate = re.compile(r'.*INTERNALDATE "'
         r' (?P<hour>[0-9][0-9]):(?P<min>[0-9][0-9]):(?P<sec>[0-9][0-9])'
         r' (?P<zonen>[-+])(?P<zoneh>[0-9][0-9])(?P<zonem>[0-9][0-9])'
         r'"')
-Literal = re.compile(r'.*{(?P<size>\d+)}$')
+Literal = re.compile(r'.*{(?P<size>\d+)}$', re.ASCII)
 MapCRLF = re.compile(r'\r\n|\r|\n')
 Response_code = re.compile(r'\[(?P<type>[A-Z-]+)( (?P<data>[^\]]*))?\]')
 Untagged_response = re.compile(r'\* (?P<type>[A-Z-]+)( (?P<data>.*))?')
-Untagged_status = re.compile(r'\* (?P<data>\d+) (?P<type>[A-Z-]+)( (?P<data2>.*))?')
+Untagged_status = re.compile(
+    r'\* (?P<data>\d+) (?P<type>[A-Z-]+)( (?P<data2>.*))?', re.ASCII)
 
 
 
@@ -146,7 +147,7 @@ class IMAP4:
     class abort(error): pass        # Service errors - close and retry
     class readonly(abort): pass     # Mailbox status changed to READ-ONLY
 
-    mustquote = re.compile(r"[^\w!#$%&'*+,.:;<=>?^`|~-]")
+    mustquote = re.compile(r"[^\w!#$%&'*+,.:;<=>?^`|~-]", re.ASCII)
 
     def __init__(self, host = '', port = IMAP4_PORT):
         self.debug = Debug
@@ -168,7 +169,7 @@ class IMAP4:
         self.tagpre = Int2AP(random.randint(4096, 65535))
         self.tagre = re.compile(r'(?P<tag>'
                         + self.tagpre
-                        + r'\d+) (?P<type>[A-Z]+) (?P<data>.*)')
+                        + r'\d+) (?P<type>[A-Z]+) (?P<data>.*)', re.ASCII)
 
         # Get server welcome message,
         # request and store CAPABILITY response.
diff --git a/Lib/json/decoder.py b/Lib/json/decoder.py
index 5283eae..f0bc245 100644
--- a/Lib/json/decoder.py
+++ b/Lib/json/decoder.py
@@ -67,7 +67,7 @@ def JSONNumber(match, context):
         fn = getattr(context, 'parse_int', None) or int
         res = fn(integer)
     return res, None
-pattern(r'(-?(?:0|[1-9]\d*))(\.\d+)?([eE][-+]?\d+)?')(JSONNumber)
+pattern(r'(-?(?:0|[1-9][0-9]*))(\.[0-9]+)?([eE][-+]?[0-9]+)?')(JSONNumber)
 
 
 STRINGCHUNK = re.compile(r'(.*?)(["\\\x00-\x1f])', FLAGS)
diff --git a/Lib/logging/handlers.py b/Lib/logging/handlers.py
index 1e69120..19fb959 100644
--- a/Lib/logging/handlers.py
+++ b/Lib/logging/handlers.py
@@ -199,7 +199,7 @@ class TimedRotatingFileHandler(BaseRotatingHandler):
         else:
             raise ValueError("Invalid rollover interval specified: %s" % self.when)
 
-        self.extMatch = re.compile(self.extMatch)
+        self.extMatch = re.compile(self.extMatch, re.ASCII)
         self.interval = self.interval * interval # multiply by units requested
         self.rolloverAt = currentTime + self.interval
 
diff --git a/Lib/platform.py b/Lib/platform.py
index ff81d28..0182180 100755
--- a/Lib/platform.py
+++ b/Lib/platform.py
@@ -118,7 +118,7 @@ _libc_search = re.compile(r'(__libc_init)'
                           '|'
                           '(GLIBC_([0-9.]+))'
                           '|'
-                          '(libc(_\w+)?\.so(?:\.(\d[0-9.]*))?)')
+                          '(libc(_\w+)?\.so(?:\.(\d[0-9.]*))?)', re.ASCII)
 
 def libc_ver(executable=sys.executable,lib='',version='',
 
@@ -223,15 +223,15 @@ def _dist_try_harder(distname,version,id):
 
     return distname,version,id
 
-_release_filename = re.compile(r'(\w+)[-_](release|version)')
+_release_filename = re.compile(r'(\w+)[-_](release|version)', re.ASCII)
 _lsb_release_version = re.compile(r'(.+)'
                                    ' release '
                                    '([\d.]+)'
-                                   '[^(]*(?:\((.+)\))?')
+                                   '[^(]*(?:\((.+)\))?', re.ASCII)
 _release_version = re.compile(r'([^0-9]+)'
                                '(?: release )?'
                                '([\d.]+)'
-                               '[^(]*(?:\((.+)\))?')
+                               '[^(]*(?:\((.+)\))?', re.ASCII)
 
 # See also http://www.novell.com/coolsolutions/feature/11251.html
 # and http://linuxmafia.com/faq/Admin/release-files.html
@@ -464,7 +464,7 @@ def _norm_version(version, build=''):
 
 _ver_output = re.compile(r'(?:([\w ]+) ([\w.]+) '
                          '.*'
-                         'Version ([\d.]+))')
+                         'Version ([\d.]+))', re.ASCII)
 
 def _syscmd_ver(system='', release='', version='',
 
@@ -1253,16 +1253,16 @@ def processor():
 _sys_version_parser = re.compile(
     r'([\w.+]+)\s*'
     '\(#?([^,]+),\s*([\w ]+),\s*([\w :]+)\)\s*'
-    '\[([^\]]+)\]?')
+    '\[([^\]]+)\]?', re.ASCII)
 
 _jython_sys_version_parser = re.compile(
-    r'([\d\.]+)')
+    r'([\d\.]+)', re.ASCII)
 
 _ironpython_sys_version_parser = re.compile(
     r'IronPython\s*'
     '([\d\.]+)'
     '(?: \(([\d\.]+)\))?'
-    ' on (.NET [\d\.]+)')
+    ' on (.NET [\d\.]+)', re.ASCII)
 
 _sys_version_cache = {}
 
diff --git a/Lib/plistlib.py b/Lib/plistlib.py
index b775324..83e5d04 100644
--- a/Lib/plistlib.py
+++ b/Lib/plistlib.py
@@ -147,7 +147,7 @@ class DumbXMLWriter:
 # Contents should conform to a subset of ISO 8601
 # (in particular, YYYY '-' MM '-' DD 'T' HH ':' MM ':' SS 'Z'.  Smaller units may be omitted with
 #  a loss of precision)
-_dateParser = re.compile(r"(?P<year>\d\d\d\d)(?:-(?P<month>\d\d)(?:-(?P<day>\d\d)(?:T(?P<hour>\d\d)(?::(?P<minute>\d\d)(?::(?P<second>\d\d))?)?)?)?)?Z")
+_dateParser = re.compile(r"(?P<year>\d\d\d\d)(?:-(?P<month>\d\d)(?:-(?P<day>\d\d)(?:T(?P<hour>\d\d)(?::(?P<minute>\d\d)(?::(?P<second>\d\d))?)?)?)?)?Z", re.ASCII)
 
 def _dateFromString(s):
     order = ('year', 'month', 'day', 'hour', 'minute', 'second')
diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index dc0aa10..575492f 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -241,7 +241,7 @@ def expandvars(path):
         return path
     if not _varprog:
         import re
-        _varprog = re.compile(r'\$(\w+|\{[^}]*\})')
+        _varprog = re.compile(r'\$(\w+|\{[^}]*\})', re.ASCII)
     i = 0
     while True:
         m = _varprog.search(path, i)
diff --git a/Lib/py_compile.py b/Lib/py_compile.py
index 8ef3662..cce5ac1 100644
--- a/Lib/py_compile.py
+++ b/Lib/py_compile.py
@@ -86,7 +86,7 @@ def read_encoding(file, default):
             line = f.readline()
             if not line:
                 break
-            m = re.match(r".*\bcoding:\s*(\S+)\b", line)
+            m = re.match(br".*\bcoding:\s*(\S+)\b", line)
             if m:
                 return m.group(1).decode("ascii")
         return default
diff --git a/Lib/re.py b/Lib/re.py
index 951f239..63a95fd 100644
--- a/Lib/re.py
+++ b/Lib/re.py
@@ -44,7 +44,7 @@ The special characters are:
     "|"      A|B, creates an RE that will match either A or B.
     (...)    Matches the RE inside the parentheses.
              The contents can be retrieved or matched later in the string.
-    (?iLmsux) Set the I, L, M, S, U, or X flag for the RE (see below).
+    (?aiLmsux) Set the A, I, L, M, S, U, or X flag for the RE (see below).
     (?:...)  Non-grouping version of regular parentheses.
     (?P<name>...) The substring matched by the group is accessible by name.
     (?P=name)     Matches the text matched earlier by the group named name.
@@ -64,11 +64,18 @@ resulting RE will match the second character.
     \Z       Matches only at the end of the string.
     \b       Matches the empty string, but only at the start or end of a word.
     \B       Matches the empty string, but not at the start or end of a word.
-    \d       Matches any decimal digit; equivalent to the set [0-9].
-    \D       Matches any non-digit character; equivalent to the set [^0-9].
+    \d       Matches any decimal digit; equivalent to the set [0-9] in
+             bytes patterns or string patterns with the ASCII flag.
+             In string patterns without the ASCII flag, it will match the whole
+             range of Unicode digits.
+    \D       Matches any non-digit character; equivalent to [^\d].
     \s       Matches any whitespace character; equivalent to [ \t\n\r\f\v].
     \S       Matches any non-whitespace character; equiv. to [^ \t\n\r\f\v].
-    \w       Matches any alphanumeric character; equivalent to [a-zA-Z0-9_].
+    \w       Matches any alphanumeric character; equivalent to [a-zA-Z0-9_]
+             in bytes patterns or string patterns with the ASCII flag.
+             In string patterns without the ASCII flag, it will match the
+             range of Unicode alphanumeric characters (letters plus digits
+             plus underscore).
              With LOCALE, it will match the set [0-9_] plus characters defined
              as letters for the current locale.
     \W       Matches the complement of \w.
@@ -87,6 +94,12 @@ This module exports the following functions:
     escape   Backslash all non-alphanumerics in a string.
 
 Some of the functions in this module takes flags as optional parameters:
+    A  ASCII       For string patterns, make \w, \W, \b, \B, \d, \D
+                   match the corresponding ASCII character categories
+                   (rather than the whole Unicode categories, which is the
+                   default).
+                   For bytes patterns, this flag is the only available
+                   behaviour and needn't be specified.
     I  IGNORECASE  Perform case-insensitive matching.
     L  LOCALE      Make \w, \W, \b, \B, dependent on the current locale.
     M  MULTILINE   "^" matches the beginning of lines (after a newline)
@@ -95,7 +108,8 @@ Some of the functions in this module takes flags as optional parameters:
                    as the end of the string.
     S  DOTALL      "." matches any character at all, including the newline.
     X  VERBOSE     Ignore whitespace and comments for nicer looking RE's.
-    U  UNICODE     Make \w, \W, \b, \B, dependent on the Unicode locale.
+    U  UNICODE     For compatibility only. Ignored for string patterns (it
+                   is the default), and forbidden for bytes patterns.
 
 This module also defines an exception 'error'.
 
@@ -107,16 +121,17 @@ import sre_parse
 
 # public symbols
 __all__ = [ "match", "search", "sub", "subn", "split", "findall",
-    "compile", "purge", "template", "escape", "I", "L", "M", "S", "X",
-    "U", "IGNORECASE", "LOCALE", "MULTILINE", "DOTALL", "VERBOSE",
+    "compile", "purge", "template", "escape", "A", "I", "L", "M", "S", "X",
+    "U", "ASCII", "IGNORECASE", "LOCALE", "MULTILINE", "DOTALL", "VERBOSE",
     "UNICODE", "error" ]
 
 __version__ = "2.2.1"
 
 # flags
+A = ASCII = sre_compile.SRE_FLAG_ASCII # assume ascii "locale"
 I = IGNORECASE = sre_compile.SRE_FLAG_IGNORECASE # ignore case
 L = LOCALE = sre_compile.SRE_FLAG_LOCALE # assume current 8-bit locale
-U = UNICODE = sre_compile.SRE_FLAG_UNICODE # assume unicode locale
+U = UNICODE = sre_compile.SRE_FLAG_UNICODE # assume unicode "locale"
 M = MULTILINE = sre_compile.SRE_FLAG_MULTILINE # make anchors look for newline
 S = DOTALL = sre_compile.SRE_FLAG_DOTALL # make dot match newline
 X = VERBOSE = sre_compile.SRE_FLAG_VERBOSE # ignore whitespace and comments
diff --git a/Lib/sre_constants.py b/Lib/sre_constants.py
index 94962cb..6cf69c3 100644
--- a/Lib/sre_constants.py
+++ b/Lib/sre_constants.py
@@ -207,9 +207,10 @@ SRE_FLAG_IGNORECASE = 2 # case insensitive
 SRE_FLAG_LOCALE = 4 # honour system locale
 SRE_FLAG_MULTILINE = 8 # treat target as multiline string
 SRE_FLAG_DOTALL = 16 # treat target as a single string
-SRE_FLAG_UNICODE = 32 # use unicode locale
+SRE_FLAG_UNICODE = 32 # use unicode "locale"
 SRE_FLAG_VERBOSE = 64 # ignore whitespace and comments
 SRE_FLAG_DEBUG = 128 # debugging
+SRE_FLAG_ASCII = 256 # use ascii "locale"
 
 # flags for INFO primitive
 SRE_INFO_PREFIX = 1 # has prefix
diff --git a/Lib/sre_parse.py b/Lib/sre_parse.py
index ffa8902..9d6e631 100644
--- a/Lib/sre_parse.py
+++ b/Lib/sre_parse.py
@@ -64,6 +64,7 @@ FLAGS = {
     "s": SRE_FLAG_DOTALL,
     "x": SRE_FLAG_VERBOSE,
     # extensions
+    "a": SRE_FLAG_ASCII,
     "t": SRE_FLAG_TEMPLATE,
     "u": SRE_FLAG_UNICODE,
 }
@@ -672,6 +673,18 @@ def _parse(source, state):
 
     return subpattern
 
+def fix_flags(src, flags):
+    # Check and fix flags according to the type of pattern (str or bytes)
+    if isinstance(src, str):
+        if not flags & SRE_FLAG_ASCII:
+            flags |= SRE_FLAG_UNICODE
+        elif flags & SRE_FLAG_UNICODE:
+            raise ValueError("ASCII and UNICODE flags are incompatible")
+    else:
+        if flags & SRE_FLAG_UNICODE:
+            raise ValueError("can't use UNICODE flag with a bytes pattern")
+    return flags
+
 def parse(str, flags=0, pattern=None):
     # parse 're' pattern into list of (opcode, argument) tuples
 
@@ -683,6 +696,7 @@ def parse(str, flags=0, pattern=None):
     pattern.str = str
 
     p = _parse_sub(source, pattern, 0)
+    p.pattern.flags = fix_flags(str, p.pattern.flags)
 
     tail = source.get()
     if tail == ")":
diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index ecb32f6..222b433 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -1368,7 +1368,7 @@ class TarInfo(object):
         # "%d %s=%s\n" % (length, keyword, value). length is the size
         # of the complete record including the length field itself and
         # the newline. keyword and value are both UTF-8 encoded strings.
-        regex = re.compile(r"(\d+) ([^=]+)=", re.U)
+        regex = re.compile(br"(\d+) ([^=]+)=")
         pos = 0
         while True:
             match = regex.match(buf, pos)
diff --git a/Lib/test/re_tests.py b/Lib/test/re_tests.py
index 220301a..d314e20 100755
--- a/Lib/test/re_tests.py
+++ b/Lib/test/re_tests.py
@@ -667,4 +667,4 @@ tests.extend([
     (r'\b.\b', 'a', SUCCEED, 'found', 'a'),
     (r'(?u)\b.\b', u, SUCCEED, 'found', u),
     (r'(?u)\w', u, SUCCEED, 'found', u),
-    ])
+])
diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index c64ac19..630f862 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -506,7 +506,7 @@ class ByteArrayTest(BaseBytesTest):
         def by(s):
             return bytearray(map(ord, s))
         b = by("Hello, world")
-        self.assertEqual(re.findall(r"\w+", b), [by("Hello"), by("world")])
+        self.assertEqual(re.findall(br"\w+", b), [by("Hello"), by("world")])
 
     def test_setitem(self):
         b = bytearray([1, 2, 3])
diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
index 0b5202a..9fe044f 100644
--- a/Lib/test/test_mmap.py
+++ b/Lib/test/test_mmap.py
@@ -54,7 +54,7 @@ class MmapTests(unittest.TestCase):
         m.flush()
 
         # Test doing a regular expression match in an mmap'ed file
-        match = re.search('[A-Za-z]+', m)
+        match = re.search(b'[A-Za-z]+', m)
         if match is None:
             self.fail('regex match on mmap failed!')
         else:
diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index 60b816e..755cb00 100644
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -83,23 +83,6 @@ class ReTests(unittest.TestCase):
         self.assertEqual(re.sub('\r\n', '\n', 'abc\r\ndef\r\n'),
                          'abc\ndef\n')
 
-    def test_bug_1140(self):
-        # re.sub(x, y, b'') should return b'', not '', and
-        # re.sub(x, y, '') should return '', not b''.
-        # Also:
-        # re.sub(x, y, str(x)) should return str(y), and
-        # re.sub(x, y, bytes(x)) should return
-        #     str(y) if isinstance(y, str) else unicode(y).
-        for x in 'x',  b'x':
-            for y in 'y', b'y':
-                z = re.sub(x, y, b'')
-                self.assertEqual(z, b'')
-                self.assertEqual(type(z), bytes)
-                #
-                z = re.sub(x, y, '')
-                self.assertEqual(z, '')
-                self.assertEqual(type(z), str)
-
     def test_bug_1661(self):
         # Verify that flags do not get silently ignored with compiled patterns
         pattern = re.compile('.')
@@ -327,7 +310,7 @@ class ReTests(unittest.TestCase):
 
     def test_getattr(self):
         self.assertEqual(re.compile("(?i)(a)(b)").pattern, "(?i)(a)(b)")
-        self.assertEqual(re.compile("(?i)(a)(b)").flags, re.I)
+        self.assertEqual(re.compile("(?i)(a)(b)").flags, re.I | re.U)
         self.assertEqual(re.compile("(?i)(a)(b)").groups, 2)
         self.assertEqual(re.compile("(?i)(a)(b)").groupindex, {})
         self.assertEqual(re.compile("(?i)(?P<first>a)(?P<other>b)").groupindex,
@@ -614,8 +597,8 @@ class ReTests(unittest.TestCase):
         import array
         for typecode in 'bBuhHiIlLfd':
             a = array.array(typecode)
-            self.assertEqual(re.compile("bla").match(a), None)
-            self.assertEqual(re.compile("").match(a).groups(), ())
+            self.assertEqual(re.compile(b"bla").match(a), None)
+            self.assertEqual(re.compile(b"").match(a).groups(), ())
 
     def test_inline_flags(self):
         # Bug #1700
@@ -658,6 +641,48 @@ class ReTests(unittest.TestCase):
         self.assertEqual(pattern.sub('#', 'a\nb\nc'), 'a#\nb#\nc#')
         self.assertEqual(pattern.sub('#', '\n'), '#\n#')
 
+    def test_bytes_str_mixing(self):
+        # Mixing str and bytes is disallowed
+        pat = re.compile('.')
+        bpat = re.compile(b'.')
+        self.assertRaises(TypeError, pat.match, b'b')
+        self.assertRaises(TypeError, bpat.match, 'b')
+        self.assertRaises(TypeError, pat.sub, b'b', 'c')
+        self.assertRaises(TypeError, pat.sub, 'b', b'c')
+        self.assertRaises(TypeError, pat.sub, b'b', b'c')
+        self.assertRaises(TypeError, bpat.sub, b'b', 'c')
+        self.assertRaises(TypeError, bpat.sub, 'b', b'c')
+        self.assertRaises(TypeError, bpat.sub, 'b', 'c')
+
+    def test_ascii_and_unicode_flag(self):
+        # String patterns
+        for flags in (0, re.UNICODE):
+            pat = re.compile('\xc0', flags | re.IGNORECASE)
+            self.assertNotEqual(pat.match('\xe0'), None)
+            pat = re.compile('\w', flags)
+            self.assertNotEqual(pat.match('\xe0'), None)
+        pat = re.compile('\xc0', re.ASCII | re.IGNORECASE)
+        self.assertEqual(pat.match('\xe0'), None)
+        pat = re.compile('(?a)\xc0', re.IGNORECASE)
+        self.assertEqual(pat.match('\xe0'), None)
+        pat = re.compile('\w', re.ASCII)
+        self.assertEqual(pat.match('\xe0'), None)
+        pat = re.compile('(?a)\w')
+        self.assertEqual(pat.match('\xe0'), None)
+        # Bytes patterns
+        for flags in (0, re.ASCII):
+            pat = re.compile(b'\xc0', re.IGNORECASE)
+            self.assertEqual(pat.match(b'\xe0'), None)
+            pat = re.compile(b'\w')
+            self.assertEqual(pat.match(b'\xe0'), None)
+        # Incompatibilities
+        self.assertRaises(ValueError, re.compile, b'\w', re.UNICODE)
+        self.assertRaises(ValueError, re.compile, b'(?u)\w')
+        self.assertRaises(ValueError, re.compile, '\w', re.UNICODE | re.ASCII)
+        self.assertRaises(ValueError, re.compile, '(?u)\w', re.ASCII)
+        self.assertRaises(ValueError, re.compile, '(?a)\w', re.UNICODE)
+        self.assertRaises(ValueError, re.compile, '(?au)\w')
+
 
 def run_re_tests():
     from test.re_tests import benchmarks, tests, SUCCEED, FAIL, SYNTAX_ERROR
diff --git a/Lib/tokenize.py b/Lib/tokenize.py
index 31366de..ec5a79a 100644
--- a/Lib/tokenize.py
+++ b/Lib/tokenize.py
@@ -47,21 +47,23 @@ def group(*choices): return '(' + '|'.join(choices) + ')'
 def any(*choices): return group(*choices) + '*'
 def maybe(*choices): return group(*choices) + '?'
 
+# Note: we use unicode matching for names ("\w") but ascii matching for
+# number literals.
 Whitespace = r'[ \f\t]*'
 Comment = r'#[^\r\n]*'
 Ignore = Whitespace + any(r'\\\r?\n' + Whitespace) + maybe(Comment)
 Name = r'[a-zA-Z_]\w*'
 
-Hexnumber = r'0[xX][\da-fA-F]+'
+Hexnumber = r'0[xX][0-9a-fA-F]+'
 Binnumber = r'0[bB][01]+'
 Octnumber = r'0[oO][0-7]+'
-Decnumber = r'(?:0+|[1-9]\d*)'
+Decnumber = r'(?:0+|[1-9][0-9]*)'
 Intnumber = group(Hexnumber, Binnumber, Octnumber, Decnumber)
-Exponent = r'[eE][-+]?\d+'
-Pointfloat = group(r'\d+\.\d*', r'\.\d+') + maybe(Exponent)
-Expfloat = r'\d+' + Exponent
+Exponent = r'[eE][-+]?[0-9]+'
+Pointfloat = group(r'[0-9]+\.[0-9]*', r'\.[0-9]+') + maybe(Exponent)
+Expfloat = r'[0-9]+' + Exponent
 Floatnumber = group(Pointfloat, Expfloat)
-Imagnumber = group(r'\d+[jJ]', Floatnumber + r'[jJ]')
+Imagnumber = group(r'[0-9]+[jJ]', Floatnumber + r'[jJ]')
 Number = group(Imagnumber, Floatnumber, Intnumber)
 
 # Tail end of ' string.
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 889d9642..aaab059 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -141,7 +141,7 @@ def urlcleanup():
         _opener = None
 
 # copied from cookielib.py
-_cut_port_re = re.compile(r":\d+$")
+_cut_port_re = re.compile(r":\d+$", re.ASCII)
 def request_host(request):
     """Return request-host, as defined by RFC 2965.
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 3823772..e8fa5f5 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -30,6 +30,14 @@ Core and Builtins
 Library
 -------
 
+- Issue #2834: update the regular expression library to match the unicode
+  standards of py3k. In other words, mixing bytes and unicode strings
+  (be it as pattern, search string or replacement string) raises a TypeError.
+  Moreover, the re.UNICODE flag is enabled automatically for unicode patterns,
+  and can be disabled by specifying a new re.ASCII flag; as for bytes
+  patterns, ASCII matching is the only option and trying to specify re.UNICODE
+  for such patterns raises a ValueError.
+
 - Issue #3300: make urllib.parse.[un]quote() default to UTF-8.
   Code contributed by Matt Giuca.  quote() now encodes the input
   before quoting, unquote() decodes after unquoting.  There are
diff --git a/Modules/_sre.c b/Modules/_sre.c
index 64fc513..2a54d8e 100644
--- a/Modules/_sre.c
+++ b/Modules/_sre.c
@@ -1691,7 +1691,7 @@ getstring(PyObject* string, Py_ssize_t* p_length, int* p_charsize)
     /* get pointer to string buffer */
     view.len = -1;
     buffer = Py_TYPE(string)->tp_as_buffer;
-    if (!buffer || !buffer->bf_getbuffer || 
+    if (!buffer || !buffer->bf_getbuffer ||
         (*buffer->bf_getbuffer)(string, &view, PyBUF_SIMPLE) < 0) {
             PyErr_SetString(PyExc_TypeError, "expected string or buffer");
             return NULL;
@@ -1717,7 +1717,7 @@ getstring(PyObject* string, Py_ssize_t* p_length, int* p_charsize)
     if (PyBytes_Check(string) || bytes == size)
         charsize = 1;
 #if defined(HAVE_UNICODE)
-    else if (bytes == (Py_ssize_t) (size * sizeof(Py_UNICODE))) 
+    else if (bytes == (Py_ssize_t) (size * sizeof(Py_UNICODE)))
         charsize = sizeof(Py_UNICODE);
 #endif
     else {
@@ -1729,7 +1729,7 @@ getstring(PyObject* string, Py_ssize_t* p_length, int* p_charsize)
     *p_charsize = charsize;
 
     if (ptr == NULL) {
-            PyErr_SetString(PyExc_ValueError, 
+            PyErr_SetString(PyExc_ValueError,
                             "Buffer is NULL");
     }
     return ptr;
@@ -1754,6 +1754,17 @@ state_init(SRE_STATE* state, PatternObject* pattern, PyObject* string,
     if (!ptr)
         return NULL;
 
+	if (charsize == 1 && pattern->charsize > 1) {
+		PyErr_SetString(PyExc_TypeError,
+			"can't use a string pattern on a bytes-like object");
+		return NULL;
+	}
+	if (charsize > 1 && pattern->charsize == 1) {
+		PyErr_SetString(PyExc_TypeError,
+			"can't use a bytes pattern on a string-like object");
+		return NULL;
+	}
+
     /* adjust boundaries */
     if (start < 0)
         start = 0;
@@ -2682,6 +2693,16 @@ _compile(PyObject* self_, PyObject* args)
         return NULL;
     }
 
+	if (pattern == Py_None)
+		self->charsize = -1;
+	else {
+		Py_ssize_t p_length;
+		if (!getstring(pattern, &p_length, &self->charsize)) {
+			PyObject_DEL(self);
+			return NULL;
+		}
+	}
+
     Py_INCREF(pattern);
     self->pattern = pattern;
 
diff --git a/Modules/sre.h b/Modules/sre.h
index d4af05c..518c11d 100644
--- a/Modules/sre.h
+++ b/Modules/sre.h
@@ -30,6 +30,7 @@ typedef struct {
     PyObject* pattern; /* pattern source (or None) */
     int flags; /* flags used when compiling pattern source */
     PyObject *weakreflist; /* List of weak references */
+	int charsize; /* pattern charsize (or -1) */
     /* pattern code */
     Py_ssize_t codesize;
     SRE_CODE code[1];