- Issue #719888: Updated tokenize to use a bytes API. generate_tokens has been

  renamed tokenize and now works with bytes rather than strings. A new
  detect_encoding function has been added for determining source file encoding
  according to PEP-0263. Token sequences returned by tokenize always start
  with an ENCODING token which specifies the encoding used to decode the file.
  This token is used to encode the output of untokenize back to bytes.

Credit goes to Michael "I'm-going-to-name-my-first-child-unittest" Foord from Resolver Systems for this work.

16 files changed, 610 insertions, 183 deletions

diff --git a/Doc/ACKS.txt b/Doc/ACKS.txt
index 7344cf8..5e97e33 100644
--- a/Doc/ACKS.txt
+++ b/Doc/ACKS.txt
@@ -209,3 +209,5 @@ docs@python.org), and we'll be glad to correct the problem.
    * Moshe Zadka
    * Milan Zamazal
    * Cheng Zhang
+   * Trent Nelson
+   * Michael Foord
diff --git a/Doc/library/tokenize.rst b/Doc/library/tokenize.rst
index 9a17b14..bbe73d0 100644
--- a/Doc/library/tokenize.rst
+++ b/Doc/library/tokenize.rst
@@ -9,50 +9,34 @@
 
 
 The :mod:`tokenize` module provides a lexical scanner for Python source code,
-implemented in Python.  The scanner in this module returns comments as tokens as
-well, making it useful for implementing "pretty-printers," including colorizers
-for on-screen displays.
+implemented in Python.  The scanner in this module returns comments as tokens
+as well, making it useful for implementing "pretty-printers," including
+colorizers for on-screen displays.
 
 The primary entry point is a :term:`generator`:
 
 
-.. function:: generate_tokens(readline)
+.. function:: tokenize(readline)
 
-   The :func:`generate_tokens` generator requires one argument, *readline*, which
+   The :func:`tokenize` generator requires one argument, *readline*, which
    must be a callable object which provides the same interface as the
    :meth:`readline` method of built-in file objects (see section
-   :ref:`bltin-file-objects`).  Each call to the function should return one line of
-   input as a string.
+   :ref:`bltin-file-objects`).  Each call to the function should return one 
+   line of input as bytes.
 
-   The generator produces 5-tuples with these members: the token type; the token
-   string; a 2-tuple ``(srow, scol)`` of ints specifying the row and column where
-   the token begins in the source; a 2-tuple ``(erow, ecol)`` of ints specifying
-   the row and column where the token ends in the source; and the line on which the
-   token was found. The line passed is the *logical* line; continuation lines are
-   included.
-
-
-An older entry point is retained for backward compatibility:
-
-.. function:: tokenize(readline[, tokeneater])
-
-   The :func:`tokenize` function accepts two parameters: one representing the input
-   stream, and one providing an output mechanism for :func:`tokenize`.
-
-   The first parameter, *readline*, must be a callable object which provides the
-   same interface as the :meth:`readline` method of built-in file objects (see
-   section :ref:`bltin-file-objects`).  Each call to the function should return one
-   line of input as a string. Alternately, *readline* may be a callable object that
-   signals completion by raising :exc:`StopIteration`.
-
-   The second parameter, *tokeneater*, must also be a callable object.  It is
-   called once for each token, with five arguments, corresponding to the tuples
-   generated by :func:`generate_tokens`.
+   The generator produces 5-tuples with these members: the token type; the 
+   token string; a 2-tuple ``(srow, scol)`` of ints specifying the row and 
+   column where the token begins in the source; a 2-tuple ``(erow, ecol)`` of 
+   ints specifying the row and column where the token ends in the source; and 
+   the line on which the token was found. The line passed is the *logical* 
+   line; continuation lines are included.
+   
+   tokenize determines the source encoding of the file by looking for a utf-8
+   bom or encoding cookie, according to :pep:`263`.
 
 
 All constants from the :mod:`token` module are also exported from
-:mod:`tokenize`, as are two additional token type values that might be passed to
-the *tokeneater* function by :func:`tokenize`:
+:mod:`tokenize`, as are three additional token type values:
 
 .. data:: COMMENT
 
@@ -62,55 +46,95 @@ the *tokeneater* function by :func:`tokenize`:
 .. data:: NL
 
    Token value used to indicate a non-terminating newline.  The NEWLINE token
-   indicates the end of a logical line of Python code; NL tokens are generated when
-   a logical line of code is continued over multiple physical lines.
+   indicates the end of a logical line of Python code; NL tokens are generated 
+   when a logical line of code is continued over multiple physical lines.
 
-Another function is provided to reverse the tokenization process. This is useful
-for creating tools that tokenize a script, modify the token stream, and write
-back the modified script.
 
+.. data:: ENCODING
 
-.. function:: untokenize(iterable)
+    Token value that indicates the encoding used to decode the source bytes 
+    into text. The first token returned by :func:`tokenize` will always be an 
+    ENCODING token.
 
-   Converts tokens back into Python source code.  The *iterable* must return
-   sequences with at least two elements, the token type and the token string.  Any
-   additional sequence elements are ignored.
 
-   The reconstructed script is returned as a single string.  The result is
-   guaranteed to tokenize back to match the input so that the conversion is
-   lossless and round-trips are assured.  The guarantee applies only to the token
-   type and token string as the spacing between tokens (column positions) may
-   change.
+Another function is provided to reverse the tokenization process. This is 
+useful for creating tools that tokenize a script, modify the token stream, and 
+write back the modified script.
 
 
+.. function:: untokenize(iterable)
+
+    Converts tokens back into Python source code.  The *iterable* must return
+    sequences with at least two elements, the token type and the token string. 
+    Any additional sequence elements are ignored.
+    
+    The reconstructed script is returned as a single string.  The result is
+    guaranteed to tokenize back to match the input so that the conversion is
+    lossless and round-trips are assured.  The guarantee applies only to the 
+    token type and token string as the spacing between tokens (column 
+    positions) may change.
+    
+    It returns bytes, encoded using the ENCODING token, which is the first 
+    token sequence output by :func:`tokenize`.
+
+
+:func:`tokenize` needs to detect the encoding of source files it tokenizes. The
+function it uses to do this is available:
+
+.. function:: detect_encoding(readline)
+
+    The :func:`detect_encoding` function is used to detect the encoding that 
+    should be used to decode a Python source file. It requires one argment, 
+    readline, in the same way as the :func:`tokenize` generator.
+    
+    It will call readline a maximum of twice, and return the encoding used
+    (as a string) and a list of any lines (not decoded from bytes) it has read
+    in.
+    
+    It detects the encoding from the presence of a utf-8 bom or an encoding
+    cookie as specified in pep-0263. If both a bom and a cookie are present,
+    but disagree, a SyntaxError will be raised.
+    
+    If no encoding is specified, then the default of 'utf-8' will be returned. 
+
+    
 Example of a script re-writer that transforms float literals into Decimal
 objects::
 
-   def decistmt(s):
-       """Substitute Decimals for floats in a string of statements.
-
-       >>> from decimal import Decimal
-       >>> s = 'print(+21.3e-5*-.1234/81.7)'
-       >>> decistmt(s)
-       "print(+Decimal ('21.3e-5')*-Decimal ('.1234')/Decimal ('81.7'))"
-
-       >>> exec(s)
-       -3.21716034272e-007
-       >>> exec(decistmt(s))
-       -3.217160342717258261933904529E-7
-
-       """
-       result = []
-       g = generate_tokens(StringIO(s).readline)   # tokenize the string
-       for toknum, tokval, _, _, _  in g:
-           if toknum == NUMBER and '.' in tokval:  # replace NUMBER tokens
-               result.extend([
-                   (NAME, 'Decimal'),
-                   (OP, '('),
-                   (STRING, repr(tokval)),
-                   (OP, ')')
-               ])
-           else:
-               result.append((toknum, tokval))
-       return untokenize(result)
+    def decistmt(s):
+        """Substitute Decimals for floats in a string of statements.
+    
+        >>> from decimal import Decimal
+        >>> s = 'print(+21.3e-5*-.1234/81.7)'
+        >>> decistmt(s)
+        "print (+Decimal ('21.3e-5')*-Decimal ('.1234')/Decimal ('81.7'))"
+    
+        The format of the exponent is inherited from the platform C library.
+        Known cases are "e-007" (Windows) and "e-07" (not Windows).  Since
+        we're only showing 12 digits, and the 13th isn't close to 5, the
+        rest of the output should be platform-independent.
+    
+        >>> exec(s) #doctest: +ELLIPSIS
+        -3.21716034272e-0...7
+    
+        Output from calculations with Decimal should be identical across all
+        platforms.
+    
+        >>> exec(decistmt(s))
+        -3.217160342717258261933904529E-7
+        """
+        result = []
+        g = tokenize(BytesIO(s.encode('utf-8')).readline) # tokenize the string
+        for toknum, tokval, _, _, _  in g:
+            if toknum == NUMBER and '.' in tokval:  # replace NUMBER tokens
+                result.extend([
+                    (NAME, 'Decimal'),
+                    (OP, '('),
+                    (STRING, repr(tokval)),
+                    (OP, ')')
+                ])
+            else:
+                result.append((toknum, tokval))
+        return untokenize(result).decode('utf-8')
+
 
diff --git a/Doc/whatsnew/3.0.rst b/Doc/whatsnew/3.0.rst
index 219a66a..94545c5 100644
--- a/Doc/whatsnew/3.0.rst
+++ b/Doc/whatsnew/3.0.rst
@@ -392,6 +392,9 @@ details.
 * The functions :func:`os.tmpnam`, :func:`os.tempnam` and :func:`os.tmpfile`
   have been removed in favor of the :mod:`tempfile` module.
 
+* The :mod:`tokenize` module has been changed to work with bytes.  The main
+  entry point is now :func:`tokenize.tokenize`, instead of generate_tokens.
+
 .. ======================================================================
 .. whole new modules get described in subsections here
 
diff --git a/Lib/idlelib/EditorWindow.py b/Lib/idlelib/EditorWindow.py
index e1d9ba3..2b5c527 100644
--- a/Lib/idlelib/EditorWindow.py
+++ b/Lib/idlelib/EditorWindow.py
@@ -1437,7 +1437,9 @@ class IndentSearcher(object):
         _tokenize.tabsize = self.tabwidth
         try:
             try:
-                _tokenize.tokenize(self.readline, self.tokeneater)
+                tokens = _tokenize.generate_tokens(self.readline)
+                for token in tokens:
+                    self.tokeneater(*token)
             except _tokenize.TokenError:
                 # since we cut off the tokenizer early, we can trigger
                 # spurious errors
diff --git a/Lib/inspect.py b/Lib/inspect.py
index ceaea5a..5cb958b 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -657,7 +657,9 @@ def getblock(lines):
     """Extract the block of code at the top of the given list of lines."""
     blockfinder = BlockFinder()
     try:
-        tokenize.tokenize(iter(lines).__next__, blockfinder.tokeneater)
+        tokens = tokenize.generate_tokens(iter(lines).__next__)
+        for _token in tokens:
+            blockfinder.tokeneater(*_token)
     except (EndOfBlock, IndentationError):
         pass
     return lines[:blockfinder.last]
diff --git a/Lib/test/test_tokenize.py b/Lib/test/test_tokenize.py
index 2938520..308158f 100644
--- a/Lib/test/test_tokenize.py
+++ b/Lib/test/test_tokenize.py
@@ -1,13 +1,14 @@
+# -*- coding: utf-8 -*-
+
 doctests = """
 Tests for the tokenize module.
 
-    >>> import glob, random, sys
-
 The tests can be really simple. Given a small fragment of source
 code, print out a table with tokens. The ENDMARK is omitted for
 brevity.
 
     >>> dump_tokens("1 + 1")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NUMBER     '1'           (1, 0) (1, 1)
     OP         '+'           (1, 2) (1, 3)
     NUMBER     '1'           (1, 4) (1, 5)
@@ -15,6 +16,7 @@ brevity.
     >>> dump_tokens("if False:\\n"
     ...             "    # NL\\n"
     ...             "    True = False # NEWLINE\\n")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'if'          (1, 0) (1, 2)
     NAME       'False'       (1, 3) (1, 8)
     OP         ':'           (1, 8) (1, 9)
@@ -34,27 +36,12 @@ brevity.
     ...     x += 2
     ...   x += 5
     ... \"""
-    >>> for tok in generate_tokens(StringIO(indent_error_file).readline): pass
+    >>> readline = BytesIO(indent_error_file.encode('utf-8')).readline
+    >>> for tok in tokenize(readline): pass
     Traceback (most recent call last):
         ...
     IndentationError: unindent does not match any outer indentation level
 
-Test roundtrip for `untokenize`. `f` is an open file or a string. The source
-code in f is tokenized, converted back to source code via tokenize.untokenize(),
-and tokenized again from the latter. The test fails if the second tokenization
-doesn't match the first.
-
-    >>> def roundtrip(f):
-    ...     if isinstance(f, str): f = StringIO(f)
-    ...     token_list = list(generate_tokens(f.readline))
-    ...     f.close()
-    ...     tokens1 = [tok[:2] for tok in token_list]
-    ...     new_text = untokenize(tokens1)
-    ...     readline = iter(new_text.splitlines(1)).__next__
-    ...     tokens2 = [tok[:2] for tok in generate_tokens(readline)]
-    ...     return tokens1 == tokens2
-    ...
-
 There are some standard formattig practises that are easy to get right.
 
     >>> roundtrip("if x == 1:\\n"
@@ -67,14 +54,14 @@ There are some standard formattig practises that are easy to get right.
 Some people use different formatting conventions, which makes
 untokenize a little trickier. Note that this test involves trailing
 whitespace after the colon. Note that we use hex escapes to make the
-two trailing blanks apperant in the expected output.
+two trailing blanks apparent in the expected output.
 
     >>> roundtrip("if x == 1 : \\n"
     ...           "  print(x)\\n")
     True
 
     >>> f = test_support.findfile("tokenize_tests.txt")
-    >>> roundtrip(open(f))
+    >>> roundtrip(open(f, 'rb'))
     True
 
     >>> roundtrip("if x == 1:\\n"
@@ -122,27 +109,33 @@ Balancing continuation
 Ordinary integers and binary operators
 
     >>> dump_tokens("0xff <= 255")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NUMBER     '0xff'        (1, 0) (1, 4)
     OP         '<='          (1, 5) (1, 7)
     NUMBER     '255'         (1, 8) (1, 11)
     >>> dump_tokens("0b10 <= 255")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NUMBER     '0b10'        (1, 0) (1, 4)
     OP         '<='          (1, 5) (1, 7)
     NUMBER     '255'         (1, 8) (1, 11)
     >>> dump_tokens("0o123 <= 0O123")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NUMBER     '0o123'       (1, 0) (1, 5)
     OP         '<='          (1, 6) (1, 8)
     NUMBER     '0O123'       (1, 9) (1, 14)
     >>> dump_tokens("1234567 > ~0x15")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NUMBER     '1234567'     (1, 0) (1, 7)
     OP         '>'           (1, 8) (1, 9)
     OP         '~'           (1, 10) (1, 11)
     NUMBER     '0x15'        (1, 11) (1, 15)
     >>> dump_tokens("2134568 != 1231515")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NUMBER     '2134568'     (1, 0) (1, 7)
     OP         '!='          (1, 8) (1, 10)
     NUMBER     '1231515'     (1, 11) (1, 18)
     >>> dump_tokens("(-124561-1) & 200000000")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     OP         '('           (1, 0) (1, 1)
     OP         '-'           (1, 1) (1, 2)
     NUMBER     '124561'      (1, 2) (1, 8)
@@ -152,15 +145,18 @@ Ordinary integers and binary operators
     OP         '&'           (1, 12) (1, 13)
     NUMBER     '200000000'   (1, 14) (1, 23)
     >>> dump_tokens("0xdeadbeef != -1")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NUMBER     '0xdeadbeef'  (1, 0) (1, 10)
     OP         '!='          (1, 11) (1, 13)
     OP         '-'           (1, 14) (1, 15)
     NUMBER     '1'           (1, 15) (1, 16)
     >>> dump_tokens("0xdeadc0de & 12345")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NUMBER     '0xdeadc0de'  (1, 0) (1, 10)
     OP         '&'           (1, 11) (1, 12)
     NUMBER     '12345'       (1, 13) (1, 18)
     >>> dump_tokens("0xFF & 0x15 | 1234")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NUMBER     '0xFF'        (1, 0) (1, 4)
     OP         '&'           (1, 5) (1, 6)
     NUMBER     '0x15'        (1, 7) (1, 11)
@@ -170,18 +166,22 @@ Ordinary integers and binary operators
 Long integers
 
     >>> dump_tokens("x = 0")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '0'           (1, 4) (1, 5)
     >>> dump_tokens("x = 0xfffffffffff")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '0xffffffffff (1, 4) (1, 17)
     >>> dump_tokens("x = 123141242151251616110")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '123141242151 (1, 4) (1, 25)
     >>> dump_tokens("x = -15921590215012591")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     OP         '-'           (1, 4) (1, 5)
@@ -190,32 +190,39 @@ Long integers
 Floating point numbers
 
     >>> dump_tokens("x = 3.14159")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '3.14159'     (1, 4) (1, 11)
     >>> dump_tokens("x = 314159.")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '314159.'     (1, 4) (1, 11)
     >>> dump_tokens("x = .314159")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '.314159'     (1, 4) (1, 11)
     >>> dump_tokens("x = 3e14159")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '3e14159'     (1, 4) (1, 11)
     >>> dump_tokens("x = 3E123")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '3E123'       (1, 4) (1, 9)
     >>> dump_tokens("x+y = 3e-1230")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '+'           (1, 1) (1, 2)
     NAME       'y'           (1, 2) (1, 3)
     OP         '='           (1, 4) (1, 5)
     NUMBER     '3e-1230'     (1, 6) (1, 13)
     >>> dump_tokens("x = 3.14e159")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '3.14e159'    (1, 4) (1, 12)
@@ -223,6 +230,7 @@ Floating point numbers
 String literals
 
     >>> dump_tokens("x = ''; y = \\\"\\\"")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     STRING     "''"          (1, 4) (1, 6)
@@ -231,6 +239,7 @@ String literals
     OP         '='           (1, 10) (1, 11)
     STRING     '""'          (1, 12) (1, 14)
     >>> dump_tokens("x = '\\\"'; y = \\\"'\\\"")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     STRING     '\\'"\\''       (1, 4) (1, 7)
@@ -239,24 +248,28 @@ String literals
     OP         '='           (1, 11) (1, 12)
     STRING     '"\\'"'        (1, 13) (1, 16)
     >>> dump_tokens("x = \\\"doesn't \\\"shrink\\\", does it\\\"")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     STRING     '"doesn\\'t "' (1, 4) (1, 14)
     NAME       'shrink'      (1, 14) (1, 20)
     STRING     '", does it"' (1, 20) (1, 31)
     >>> dump_tokens("x = 'abc' + 'ABC'")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     STRING     "'abc'"       (1, 4) (1, 9)
     OP         '+'           (1, 10) (1, 11)
     STRING     "'ABC'"       (1, 12) (1, 17)
     >>> dump_tokens('y = "ABC" + "ABC"')
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'y'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     STRING     '"ABC"'       (1, 4) (1, 9)
     OP         '+'           (1, 10) (1, 11)
     STRING     '"ABC"'       (1, 12) (1, 17)
     >>> dump_tokens("x = r'abc' + r'ABC' + R'ABC' + R'ABC'")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     STRING     "r'abc'"      (1, 4) (1, 10)
@@ -267,6 +280,7 @@ String literals
     OP         '+'           (1, 29) (1, 30)
     STRING     "R'ABC'"      (1, 31) (1, 37)
     >>> dump_tokens('y = r"abc" + r"ABC" + R"ABC" + R"ABC"')
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'y'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     STRING     'r"abc"'      (1, 4) (1, 10)
@@ -280,6 +294,7 @@ String literals
 Operators
 
     >>> dump_tokens("def d22(a, b, c=2, d=2, *k): pass")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'def'         (1, 0) (1, 3)
     NAME       'd22'         (1, 4) (1, 7)
     OP         '('           (1, 7) (1, 8)
@@ -301,6 +316,7 @@ Operators
     OP         ':'           (1, 27) (1, 28)
     NAME       'pass'        (1, 29) (1, 33)
     >>> dump_tokens("def d01v_(a=1, *k, **w): pass")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'def'         (1, 0) (1, 3)
     NAME       'd01v_'       (1, 4) (1, 9)
     OP         '('           (1, 9) (1, 10)
@@ -321,6 +337,7 @@ Comparison
 
     >>> dump_tokens("if 1 < 1 > 1 == 1 >= 5 <= 0x15 <= 0x12 != " +
     ...             "1 and 5 in 1 not in 1 is 1 or 5 is not 1: pass")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'if'          (1, 0) (1, 2)
     NUMBER     '1'           (1, 3) (1, 4)
     OP         '<'           (1, 5) (1, 6)
@@ -357,6 +374,7 @@ Comparison
 Shift
 
     >>> dump_tokens("x = 1 << 1 >> 5")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '1'           (1, 4) (1, 5)
@@ -368,6 +386,7 @@ Shift
 Additive
 
     >>> dump_tokens("x = 1 - y + 15 - 1 + 0x124 + z + a[5]")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '1'           (1, 4) (1, 5)
@@ -390,6 +409,7 @@ Additive
 Multiplicative
 
     >>> dump_tokens("x = 1//1*1/5*12%0x12")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'x'           (1, 0) (1, 1)
     OP         '='           (1, 2) (1, 3)
     NUMBER     '1'           (1, 4) (1, 5)
@@ -407,6 +427,7 @@ Multiplicative
 Unary
 
     >>> dump_tokens("~1 ^ 1 & 1 |1 ^ -1")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     OP         '~'           (1, 0) (1, 1)
     NUMBER     '1'           (1, 1) (1, 2)
     OP         '^'           (1, 3) (1, 4)
@@ -419,6 +440,7 @@ Unary
     OP         '-'           (1, 16) (1, 17)
     NUMBER     '1'           (1, 17) (1, 18)
     >>> dump_tokens("-1*1/1+1*1//1 - ---1**1")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     OP         '-'           (1, 0) (1, 1)
     NUMBER     '1'           (1, 1) (1, 2)
     OP         '*'           (1, 2) (1, 3)
@@ -442,6 +464,7 @@ Unary
 Selector
 
     >>> dump_tokens("import sys, time\\nx = sys.modules['time'].time()")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     NAME       'import'      (1, 0) (1, 6)
     NAME       'sys'         (1, 7) (1, 10)
     OP         ','           (1, 10) (1, 11)
@@ -463,6 +486,7 @@ Selector
 Methods
 
     >>> dump_tokens("@staticmethod\\ndef foo(x,y): pass")
+    ENCODING   'utf-8'       (0, 0) (0, 0)
     OP         '@'           (1, 0) (1, 1)
     NAME       'staticmethod (1, 1) (1, 13)
     NEWLINE    '\\n'          (1, 13) (1, 14)
@@ -485,42 +509,43 @@ Backslash means line continuation, except for comments
     True
     >>> roundtrip("# Comment \\\\nx = 0")
     True
-
-    >>>
-    >>> tempdir = os.path.dirname(f) or os.curdir
-    >>> testfiles = glob.glob(os.path.join(tempdir, "test*.py"))
-    >>> if not test_support.is_resource_enabled("compiler"):
-    ...     testfiles = random.sample(testfiles, 10)
-    ...
-    >>> for testfile in testfiles:
-    ...     if not roundtrip(open(testfile)): break
-    ... else: True
-    True
 """
 
-
 from test import test_support
-from tokenize import (tokenize, untokenize, generate_tokens, NUMBER, NAME, OP,
-                     STRING, ENDMARKER, tok_name)
-from io import StringIO
-import os
+from tokenize import (tokenize, _tokenize, untokenize, NUMBER, NAME, OP,
+                     STRING, ENDMARKER, tok_name, detect_encoding)
+from io import BytesIO
+from unittest import TestCase
+import os, sys, glob
 
 def dump_tokens(s):
     """Print out the tokens in s in a table format.
 
     The ENDMARKER is omitted.
     """
-    f = StringIO(s)
-    for type, token, start, end, line in generate_tokens(f.readline):
+    f = BytesIO(s.encode('utf-8'))
+    for type, token, start, end, line in tokenize(f.readline):
         if type == ENDMARKER:
             break
         type = tok_name[type]
         print("%(type)-10.10s %(token)-13.13r %(start)s %(end)s" % locals())
 
-def roundtrip(s):
-    f = StringIO(s)
-    source = untokenize(generate_tokens(f.readline))
-    print(source, end="")
+def roundtrip(f):
+    """
+    Test roundtrip for `untokenize`. `f` is an open file or a string.
+    The source code in f is tokenized, converted back to source code via
+    tokenize.untokenize(), and tokenized again from the latter. The test
+    fails if the second tokenization doesn't match the first.
+    """
+    if isinstance(f, str):
+        f = BytesIO(f.encode('utf-8'))
+    token_list = list(tokenize(f.readline))
+    f.close()
+    tokens1 = [tok[:2] for tok in token_list]
+    new_bytes = untokenize(tokens1)
+    readline = (line for line in new_bytes.splitlines(1)).__next__
+    tokens2 = [tok[:2] for tok in tokenize(readline)]
+    return tokens1 == tokens2
 
 # This is an example from the docs, set up as a doctest.
 def decistmt(s):
@@ -545,9 +570,8 @@ def decistmt(s):
     >>> exec(decistmt(s))
     -3.217160342717258261933904529E-7
     """
-
     result = []
-    g = generate_tokens(StringIO(s).readline)   # tokenize the string
+    g = tokenize(BytesIO(s.encode('utf-8')).readline)   # tokenize the string
     for toknum, tokval, _, _, _  in g:
         if toknum == NUMBER and '.' in tokval:  # replace NUMBER tokens
             result.extend([
@@ -558,7 +582,238 @@ def decistmt(s):
             ])
         else:
             result.append((toknum, tokval))
-    return untokenize(result)
+    return untokenize(result).decode('utf-8')
+
+
+class TestTokenizerAdheresToPep0263(TestCase):
+    """
+    Test that tokenizer adheres to the coding behaviour stipulated in PEP 0263.
+    """
+
+    def _testFile(self, filename):
+        path = os.path.join(os.path.dirname(__file__), filename)
+        return roundtrip(open(path, 'rb'))
+
+    def test_utf8_coding_cookie_and_no_utf8_bom(self):
+        f = 'tokenize_tests-utf8-coding-cookie-and-utf8-bom-sig.txt'
+        self.assertTrue(self._testFile(f))
+
+    def test_latin1_coding_cookie_and_utf8_bom(self):
+        """
+        As per PEP 0263, if a file starts with a utf-8 BOM signature, the only
+        allowed encoding for the comment is 'utf-8'.  The text file used in
+        this test starts with a BOM signature, but specifies latin1 as the
+        coding, so verify that a SyntaxError is raised, which matches the
+        behaviour of the interpreter when it encounters a similar condition.
+        """
+        f = 'tokenize_tests-latin1-coding-cookie-and-utf8-bom-sig.txt'
+        self.failUnlessRaises(SyntaxError, self._testFile, f)
+
+    def test_no_coding_cookie_and_utf8_bom(self):
+        f = 'tokenize_tests-no-coding-cookie-and-utf8-bom-sig-only.txt'
+        self.assertTrue(self._testFile(f))
+
+    def test_utf8_coding_cookie_and_utf8_bom(self):
+        f = 'tokenize_tests-utf8-coding-cookie-and-utf8-bom-sig.txt'
+        self.assertTrue(self._testFile(f))
+
+
+class Test_Tokenize(TestCase):
+
+    def test__tokenize_decodes_with_specified_encoding(self):
+        literal = '"ЉЊЈЁЂ"'
+        line = literal.encode('utf-8')
+        first = False
+        def readline():
+            nonlocal first
+            if not first:
+                first = True
+                return line
+            else:
+                return b''
+
+        # skip the initial encoding token and the end token
+        tokens = list(_tokenize(readline, encoding='utf-8'))[1:-1]
+        expected_tokens = [(3, '"ЉЊЈЁЂ"', (1, 0), (1, 7), '"ЉЊЈЁЂ"')]
+        self.assertEquals(tokens, expected_tokens,
+                          "bytes not decoded with encoding")
+
+    def test__tokenize_does_not_decode_with_encoding_none(self):
+        literal = '"ЉЊЈЁЂ"'
+        first = False
+        def readline():
+            nonlocal first
+            if not first:
+                first = True
+                return literal
+            else:
+                return b''
+
+        # skip the end token
+        tokens = list(_tokenize(readline, encoding=None))[:-1]
+        expected_tokens = [(3, '"ЉЊЈЁЂ"', (1, 0), (1, 7), '"ЉЊЈЁЂ"')]
+        self.assertEquals(tokens, expected_tokens,
+                          "string not tokenized when encoding is None")
+
+
+class TestDetectEncoding(TestCase):
+
+    def get_readline(self, lines):
+        index = 0
+        def readline():
+            nonlocal index
+            if index == len(lines):
+                raise StopIteration
+            line = lines[index]
+            index += 1
+            return line
+        return readline
+
+    def test_no_bom_no_encoding_cookie(self):
+        lines = (
+            b'# something\n',
+            b'print(something)\n',
+            b'do_something(else)\n'
+        )
+        encoding, consumed_lines = detect_encoding(self.get_readline(lines))
+        self.assertEquals(encoding, 'utf-8')
+        self.assertEquals(consumed_lines, list(lines[:2]))
+
+    def test_bom_no_cookie(self):
+        lines = (
+            b'\xef\xbb\xbf# something\n',
+            b'print(something)\n',
+            b'do_something(else)\n'
+        )
+        encoding, consumed_lines = detect_encoding(self.get_readline(lines))
+        self.assertEquals(encoding, 'utf-8')
+        self.assertEquals(consumed_lines,
+                          [b'# something\n', b'print(something)\n'])
+
+    def test_cookie_first_line_no_bom(self):
+        lines = (
+            b'# -*- coding: latin-1 -*-\n',
+            b'print(something)\n',
+            b'do_something(else)\n'
+        )
+        encoding, consumed_lines = detect_encoding(self.get_readline(lines))
+        self.assertEquals(encoding, 'latin-1')
+        self.assertEquals(consumed_lines, [b'# -*- coding: latin-1 -*-\n'])
+
+    def test_matched_bom_and_cookie_first_line(self):
+        lines = (
+            b'\xef\xbb\xbf# coding=utf-8\n',
+            b'print(something)\n',
+            b'do_something(else)\n'
+        )
+        encoding, consumed_lines = detect_encoding(self.get_readline(lines))
+        self.assertEquals(encoding, 'utf-8')
+        self.assertEquals(consumed_lines, [b'# coding=utf-8\n'])
+
+    def test_mismatched_bom_and_cookie_first_line_raises_syntaxerror(self):
+        lines = (
+            b'\xef\xbb\xbf# vim: set fileencoding=ascii :\n',
+            b'print(something)\n',
+            b'do_something(else)\n'
+        )
+        readline = self.get_readline(lines)
+        self.assertRaises(SyntaxError, detect_encoding, readline)
+
+    def test_cookie_second_line_no_bom(self):
+        lines = (
+            b'#! something\n',
+            b'# vim: set fileencoding=ascii :\n',
+            b'print(something)\n',
+            b'do_something(else)\n'
+        )
+        encoding, consumed_lines = detect_encoding(self.get_readline(lines))
+        self.assertEquals(encoding, 'ascii')
+        expected = [b'#! something\n', b'# vim: set fileencoding=ascii :\n']
+        self.assertEquals(consumed_lines, expected)
+
+    def test_matched_bom_and_cookie_second_line(self):
+        lines = (
+            b'\xef\xbb\xbf#! something\n',
+            b'f# coding=utf-8\n',
+            b'print(something)\n',
+            b'do_something(else)\n'
+        )
+        encoding, consumed_lines = detect_encoding(self.get_readline(lines))
+        self.assertEquals(encoding, 'utf-8')
+        self.assertEquals(consumed_lines,
+                          [b'#! something\n', b'f# coding=utf-8\n'])
+
+    def test_mismatched_bom_and_cookie_second_line_raises_syntaxerror(self):
+        lines = (
+            b'\xef\xbb\xbf#! something\n',
+            b'# vim: set fileencoding=ascii :\n',
+            b'print(something)\n',
+            b'do_something(else)\n'
+        )
+        readline = self.get_readline(lines)
+        self.assertRaises(SyntaxError, detect_encoding, readline)
+
+    def test_short_files(self):
+        readline = self.get_readline((b'print(something)\n',))
+        encoding, consumed_lines = detect_encoding(readline)
+        self.assertEquals(encoding, 'utf-8')
+        self.assertEquals(consumed_lines, [b'print(something)\n'])
+
+        encoding, consumed_lines = detect_encoding(self.get_readline(()))
+        self.assertEquals(encoding, 'utf-8')
+        self.assertEquals(consumed_lines, [])
+
+        readline = self.get_readline((b'\xef\xbb\xbfprint(something)\n',))
+        encoding, consumed_lines = detect_encoding(readline)
+        self.assertEquals(encoding, 'utf-8')
+        self.assertEquals(consumed_lines, [b'print(something)\n'])
+
+        readline = self.get_readline((b'\xef\xbb\xbf',))
+        encoding, consumed_lines = detect_encoding(readline)
+        self.assertEquals(encoding, 'utf-8')
+        self.assertEquals(consumed_lines, [])
+
+
+class TestTokenize(TestCase):
+
+    def test_tokenize(self):
+        import tokenize as tokenize_module
+        encoding = object()
+        encoding_used = None
+        def mock_detect_encoding(readline):
+            return encoding, ['first', 'second']
+
+        def mock__tokenize(readline, encoding):
+            nonlocal encoding_used
+            encoding_used = encoding
+            out = []
+            while True:
+                next_line = readline()
+                if next_line:
+                    out.append(next_line)
+                    continue
+                return out
+
+        counter = 0
+        def mock_readline():
+            nonlocal counter
+            counter += 1
+            if counter == 5:
+                return b''
+            return counter
+
+        orig_detect_encoding = tokenize_module.detect_encoding
+        orig__tokenize = tokenize_module._tokenize
+        tokenize_module.detect_encoding = mock_detect_encoding
+        tokenize_module._tokenize = mock__tokenize
+        try:
+            results = tokenize(mock_readline)
+            self.assertEquals(list(results), ['first', 'second', 1, 2, 3, 4])
+        finally:
+            tokenize_module.detect_encoding = orig_detect_encoding
+            tokenize_module._tokenize = orig__tokenize
+
+        self.assertTrue(encoding_used, encoding)
 
 
 __test__ = {"doctests" : doctests, 'decistmt': decistmt}
@@ -566,6 +821,10 @@ __test__ = {"doctests" : doctests, 'decistmt': decistmt}
 def test_main():
     from test import test_tokenize
     test_support.run_doctest(test_tokenize, True)
+    test_support.run_unittest(TestTokenizerAdheresToPep0263)
+    test_support.run_unittest(Test_Tokenize)
+    test_support.run_unittest(TestDetectEncoding)
+    test_support.run_unittest(TestTokenize)
 
 if __name__ == "__main__":
     test_main()
diff --git a/Lib/test/tokenize_tests-latin1-coding-cookie-and-utf8-bom-sig.txt b/Lib/test/tokenize_tests-latin1-coding-cookie-and-utf8-bom-sig.txt
new file mode 100644
index 0000000..4a7582a
--- /dev/null
+++ b/Lib/test/tokenize_tests-latin1-coding-cookie-and-utf8-bom-sig.txt
@@ -0,0 +1,13 @@
+# -*- coding: latin1 -*-

+# IMPORTANT: this file has the utf-8 BOM signature '\xef\xbb\xbf' 

+# at the start of it.  Make sure this is preserved if any changes

+# are made!  Also note that the coding cookie above conflicts with

+# the presense of a utf-8 BOM signature -- this is intended.

+

+# Arbitrary encoded utf-8 text (stolen from test_doctest2.py).

+x = 'ЉЊЈЁЂ'

+def y():

+    """

+    And again in a comment.  ЉЊЈЁЂ

+    """

+    pass

diff --git a/Lib/test/tokenize_tests-no-coding-cookie-and-utf8-bom-sig-only.txt b/Lib/test/tokenize_tests-no-coding-cookie-and-utf8-bom-sig-only.txt
new file mode 100644
index 0000000..d6d8d49
--- /dev/null
+++ b/Lib/test/tokenize_tests-no-coding-cookie-and-utf8-bom-sig-only.txt
@@ -0,0 +1,11 @@
+# IMPORTANT: this file has the utf-8 BOM signature '\xef\xbb\xbf' 

+# at the start of it.  Make sure this is preserved if any changes

+# are made!

+

+# Arbitrary encoded utf-8 text (stolen from test_doctest2.py).

+x = 'ЉЊЈЁЂ'

+def y():

+    """

+    And again in a comment.  ЉЊЈЁЂ

+    """

+    pass

diff --git a/Lib/test/tokenize_tests-utf8-coding-cookie-and-no-utf8-bom-sig.txt b/Lib/test/tokenize_tests-utf8-coding-cookie-and-no-utf8-bom-sig.txt
new file mode 100644
index 0000000..7aeff6b
--- /dev/null
+++ b/Lib/test/tokenize_tests-utf8-coding-cookie-and-no-utf8-bom-sig.txt
@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-

+# IMPORTANT: unlike the other test_tokenize-*.txt files, this file

+# does NOT have the utf-8 BOM signature '\xef\xbb\xbf' at the start

+# of it.  Make sure this is not added inadvertently by your editor

+# if any changes are made to this file!

+

+# Arbitrary encoded utf-8 text (stolen from test_doctest2.py).

+x = 'ЉЊЈЁЂ'

+def y():

+    """

+    And again in a comment.  ЉЊЈЁЂ

+    """

+    pass

diff --git a/Lib/test/tokenize_tests-utf8-coding-cookie-and-utf8-bom-sig.txt b/Lib/test/tokenize_tests-utf8-coding-cookie-and-utf8-bom-sig.txt
new file mode 100644
index 0000000..99b1399
--- /dev/null
+++ b/Lib/test/tokenize_tests-utf8-coding-cookie-and-utf8-bom-sig.txt
@@ -0,0 +1,12 @@
+# -*- coding: utf-8 -*-

+# IMPORTANT: this file has the utf-8 BOM signature '\xef\xbb\xbf' 

+# at the start of it.  Make sure this is preserved if any changes

+# are made!

+

+# Arbitrary encoded utf-8 text (stolen from test_doctest2.py).

+x = 'ЉЊЈЁЂ'

+def y():

+    """

+    And again in a comment.  ЉЊЈЁЂ

+    """

+    pass

diff --git a/Lib/tokenize.py b/Lib/tokenize.py
index 797b6e0..d7043b1 100644
--- a/Lib/tokenize.py
+++ b/Lib/tokenize.py
@@ -1,8 +1,11 @@
 """Tokenization help for Python programs.
 
-generate_tokens(readline) is a generator that breaks a stream of
-text into Python tokens.  It accepts a readline-like method which is called
-repeatedly to get the next line of input (or "" for EOF).  It generates
+tokenize(readline) is a generator that breaks a stream of
+bytes into Python tokens. It decodes the bytes according to
+PEP-0263 for determining source file encoding.
+
+It accepts a readline-like method which is called
+repeatedly to get the next line of input (or b"" for EOF).  It generates
 5-tuples with these members:
 
     the token type (see token.py)
@@ -13,32 +16,32 @@ repeatedly to get the next line of input (or "" for EOF).  It generates
 
 It is designed to match the working of the Python tokenizer exactly, except
 that it produces COMMENT tokens for comments and gives type OP for all
-operators
-
-Older entry points
-    tokenize_loop(readline, tokeneater)
-    tokenize(readline, tokeneater=printtoken)
-are the same, except instead of generating tokens, tokeneater is a callback
-function to which the 5 fields described above are passed as 5 arguments,
-each time a new token is found."""
+operators. Aditionally, all token lists start with an ENCODING token
+which tells you which encoding was used to decode the bytes stream."""
 
 __author__ = 'Ka-Ping Yee <ping@lfw.org>'
-__credits__ = \
-    'GvR, ESR, Tim Peters, Thomas Wouters, Fred Drake, Skip Montanaro, Raymond Hettinger'
+__credits__ = ('GvR, ESR, Tim Peters, Thomas Wouters, Fred Drake, '
+               'Skip Montanaro, Raymond Hettinger, Trent Nelson, '
+               'Michael Foord')
 
-import string, re
+import re, string, sys
 from token import *
+from codecs import lookup
+from itertools import chain, repeat
+cookie_re = re.compile("coding[:=]\s*([-\w.]+)")
 
 import token
 __all__ = [x for x in dir(token) if x[0] != '_'] + ["COMMENT", "tokenize",
-           "generate_tokens", "NL", "untokenize"]
+           "detect_encoding", "NL", "untokenize", "ENCODING"]
 del token
 
 COMMENT = N_TOKENS
 tok_name[COMMENT] = 'COMMENT'
 NL = N_TOKENS + 1
 tok_name[NL] = 'NL'
-N_TOKENS += 2
+ENCODING = N_TOKENS + 2
+tok_name[ENCODING] = 'ENCODING'
+N_TOKENS += 3
 
 def group(*choices): return '(' + '|'.join(choices) + ')'
 def any(*choices): return group(*choices) + '*'
@@ -132,33 +135,6 @@ class TokenError(Exception): pass
 
 class StopTokenizing(Exception): pass
 
-def printtoken(type, token, startrowcol, endrowcol, line): # for testing
-    (srow, scol), (erow, ecol) = startrowcol, endrowcol
-    print("%d,%d-%d,%d:\t%s\t%s" % \
-        (srow, scol, erow, ecol, tok_name[type], repr(token)))
-
-def tokenize(readline, tokeneater=printtoken):
-    """
-    The tokenize() function accepts two parameters: one representing the
-    input stream, and one providing an output mechanism for tokenize().
-
-    The first parameter, readline, must be a callable object which provides
-    the same interface as the readline() method of built-in file objects.
-    Each call to the function should return one line of input as a string.
-
-    The second parameter, tokeneater, must also be a callable object. It is
-    called once for each token, with five arguments, corresponding to the
-    tuples generated by generate_tokens().
-    """
-    try:
-        tokenize_loop(readline, tokeneater)
-    except StopTokenizing:
-        pass
-
-# backwards compatible interface
-def tokenize_loop(readline, tokeneater):
-    for token_info in generate_tokens(readline):
-        tokeneater(*token_info)
 
 class Untokenizer:
 
@@ -166,6 +142,7 @@ class Untokenizer:
         self.tokens = []
         self.prev_row = 1
         self.prev_col = 0
+        self.encoding = None
 
     def add_whitespace(self, start):
         row, col = start
@@ -180,6 +157,9 @@ class Untokenizer:
                 self.compat(t, iterable)
                 break
             tok_type, token, start, end, line = t
+            if tok_type == ENCODING:
+                self.encoding = token
+                continue
             self.add_whitespace(start)
             self.tokens.append(token)
             self.prev_row, self.prev_col = end
@@ -193,12 +173,16 @@ class Untokenizer:
         indents = []
         toks_append = self.tokens.append
         toknum, tokval = token
+
         if toknum in (NAME, NUMBER):
             tokval += ' '
         if toknum in (NEWLINE, NL):
             startline = True
         for tok in iterable:
             toknum, tokval = tok[:2]
+            if toknum == ENCODING:
+                self.encoding = tokval
+                continue
 
             if toknum in (NAME, NUMBER):
                 tokval += ' '
@@ -216,8 +200,11 @@ class Untokenizer:
                 startline = False
             toks_append(tokval)
 
+
 def untokenize(iterable):
     """Transform tokens back into Python source code.
+    It returns a bytes object, encoded using the ENCODING
+    token, which is the first token sequence output by tokenize.
 
     Each element returned by the iterable must be a token sequence
     with at least two elements, a token number and token value.  If
@@ -227,24 +214,89 @@ def untokenize(iterable):
         Untokenized source will match input source exactly
 
     Round-trip invariant for limited intput:
-        # Output text will tokenize the back to the input
-        t1 = [tok[:2] for tok in generate_tokens(f.readline)]
+        # Output bytes will tokenize the back to the input
+        t1 = [tok[:2] for tok in tokenize(f.readline)]
         newcode = untokenize(t1)
-        readline = iter(newcode.splitlines(1)).__next__
-        t2 = [tok[:2] for tokin generate_tokens(readline)]
+        readline = BytesIO(newcode).readline
+        t2 = [tok[:2] for tok in tokenize(readline)]
         assert t1 == t2
     """
     ut = Untokenizer()
-    return ut.untokenize(iterable)
+    out = ut.untokenize(iterable)
+    if ut.encoding is not None:
+        out = out.encode(ut.encoding)
+    return out
 
-def generate_tokens(readline):
+
+def detect_encoding(readline):
     """
-    The generate_tokens() generator requires one argment, readline, which
+    The detect_encoding() function is used to detect the encoding that should
+    be used to decode a Python source file. It requires one argment, readline,
+    in the same way as the tokenize() generator.
+
+    It will call readline a maximum of twice, and return the encoding used
+    (as a string) and a list of any lines (left as bytes) it has read
+    in.
+
+    It detects the encoding from the presence of a utf-8 bom or an encoding
+    cookie as specified in pep-0263. If both a bom and a cookie are present,
+    but disagree, a SyntaxError will be raised.
+
+    If no encoding is specified, then the default of 'utf-8' will be returned.
+    """
+    utf8_bom = b'\xef\xbb\xbf'
+    bom_found = False
+    encoding = None
+    def read_or_stop():
+        try:
+            return readline()
+        except StopIteration:
+            return b''
+
+    def find_cookie(line):
+        try:
+            line_string = line.decode('ascii')
+        except UnicodeDecodeError:
+            pass
+        else:
+            matches = cookie_re.findall(line_string)
+            if matches:
+                encoding = matches[0]
+                if bom_found and lookup(encoding).name != 'utf-8':
+                    # This behaviour mimics the Python interpreter
+                    raise SyntaxError('encoding problem: utf-8')
+                return encoding
+
+    first = read_or_stop()
+    if first.startswith(utf8_bom):
+        bom_found = True
+        first = first[3:]
+    if not first:
+        return 'utf-8', []
+
+    encoding = find_cookie(first)
+    if encoding:
+        return encoding, [first]
+
+    second = read_or_stop()
+    if not second:
+        return 'utf-8', [first]
+
+    encoding = find_cookie(second)
+    if encoding:
+        return encoding, [first, second]
+
+    return 'utf-8', [first, second]
+
+
+def tokenize(readline):
+    """
+    The tokenize() generator requires one argment, readline, which
     must be a callable object which provides the same interface as the
     readline() method of built-in file objects. Each call to the function
-    should return one line of input as a string.  Alternately, readline
+    should return one line of input as bytes.  Alternately, readline
     can be a callable function terminating with StopIteration:
-        readline = open(myfile).__next__    # Example of alternate readline
+        readline = open(myfile, 'rb').__next__  # Example of alternate readline
 
     The generator produces 5-tuples with these members: the token type; the
     token string; a 2-tuple (srow, scol) of ints specifying the row and
@@ -252,18 +304,38 @@ def generate_tokens(readline):
     ints specifying the row and column where the token ends in the source;
     and the line on which the token was found. The line passed is the
     logical line; continuation lines are included.
+
+    The first token sequence will always be an ENCODING token
+    which tells you which encoding was used to decode the bytes stream.
     """
+    encoding, consumed = detect_encoding(readline)
+    def readline_generator():
+        while True:
+            try:
+                yield readline()
+            except StopIteration:
+                return
+    chained = chain(consumed, readline_generator())
+    return _tokenize(chained.__next__, encoding)
+
+
+def _tokenize(readline, encoding):
     lnum = parenlev = continued = 0
     namechars, numchars = string.ascii_letters + '_', '0123456789'
     contstr, needcont = '', 0
     contline = None
     indents = [0]
 
+    if encoding is not None:
+        yield (ENCODING, encoding, (0, 0), (0, 0), '')
     while 1:                                   # loop over lines in stream
         try:
             line = readline()
         except StopIteration:
-            line = ''
+            line = b''
+
+        if encoding is not None:
+            line = line.decode(encoding)
         lnum = lnum + 1
         pos, max = 0, len(line)
 
@@ -385,7 +457,8 @@ def generate_tokens(readline):
         yield (DEDENT, '', (lnum, 0), (lnum, 0), '')
     yield (ENDMARKER, '', (lnum, 0), (lnum, 0), '')
 
-if __name__ == '__main__':                     # testing
-    import sys
-    if len(sys.argv) > 1: tokenize(open(sys.argv[1]).readline)
-    else: tokenize(sys.stdin.readline)
+
+# An undocumented, backwards compatible, API for all the places in the standard
+# library that expect to be able to use tokenize with strings
+def generate_tokens(readline):
+    return _tokenize(readline, None)
diff --git a/Misc/ACKS b/Misc/ACKS
index 1ae773f..9465d8b 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -752,3 +752,5 @@ Artur Zaprzala
 Mike Zarnstorff
 Siebren van der Zee
 Uwe Zessin
+Trent Nelson
+Michael Foord
diff --git a/Misc/NEWS b/Misc/NEWS
index db686cd..279da30 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -41,6 +41,12 @@ Library
 
 - Issue #1202: zlib.crc32 and zlib.adler32 now return an unsigned value.
 
+- Issue #719888: Updated tokenize to use a bytes API. generate_tokens has been
+  renamed tokenize and now works with bytes rather than strings. A new
+  detect_encoding function has been added for determining source file encoding
+  according to PEP-0263. Token sequences returned by tokenize always start
+  with an ENCODING token which specifies the encoding used to decode the file.
+  This token is used to encode the output of untokenize back to bytes.
 
 What's New in Python 3.0a3?
 ===========================
@@ -175,7 +181,6 @@ Library
 
 - Issue #1578: Problems in win_getpass.
 
-
 Build
 -----
 
diff --git a/Tools/i18n/pygettext.py b/Tools/i18n/pygettext.py
index bdf52e0..69a19ef 100755
--- a/Tools/i18n/pygettext.py
+++ b/Tools/i18n/pygettext.py
@@ -631,7 +631,9 @@ def main():
         try:
             eater.set_filename(filename)
             try:
-                tokenize.tokenize(fp.readline, eater)
+                tokens = tokenize.generate_tokens(fp.readline)
+                for _token in tokens:
+                    eater(*_token)
             except tokenize.TokenError as e:
                 print('%s: %s, line %d, column %d' % (
                     e.args[0], filename, e.args[1][0], e.args[1][1]),
diff --git a/Tools/scripts/checkappend.py b/Tools/scripts/checkappend.py
index 8953285..4c74ee5 100755
--- a/Tools/scripts/checkappend.py
+++ b/Tools/scripts/checkappend.py
@@ -103,7 +103,9 @@ class AppendChecker:
 
     def run(self):
         try:
-            tokenize.tokenize(self.file.readline, self.tokeneater)
+            tokens = tokenize.generate_tokens(self.file.readline)
+            for _token in tokens:
+                self.tokeneater(*_token)
         except tokenize.TokenError as msg:
             errprint("%r: Token Error: %s" % (self.fname, msg))
             self.nerrors = self.nerrors + 1
diff --git a/Tools/scripts/reindent.py b/Tools/scripts/reindent.py
index 981f63a..9a55198 100755
--- a/Tools/scripts/reindent.py
+++ b/Tools/scripts/reindent.py
@@ -173,7 +173,9 @@ class Reindenter:
         self.stats = []
 
     def run(self):
-        tokenize.tokenize(self.getline, self.tokeneater)
+        tokens = tokenize.generate_tokens(self.getline)
+        for _token in tokens:
+            self.tokeneater(*_token)
         # Remove trailing empty lines.
         lines = self.lines
         while lines and lines[-1] == "\n":