- 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.

3 files changed, 103 insertions, 74 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