100 lines
3.6 KiB
Plaintext
100 lines
3.6 KiB
Plaintext
PEP: 3120
|
||
Title: Using UTF-8 as the default source encoding
|
||
Version: $Revision$
|
||
Last-Modified: $Date$
|
||
Author: Martin von Löwis <martin@v.loewis.de>
|
||
Status: Final
|
||
Type: Standards Track
|
||
Content-Type: text/x-rst
|
||
Created: 15-Apr-2007
|
||
Python-Version: 3.0
|
||
Post-History:
|
||
|
||
|
||
Specification
|
||
=============
|
||
|
||
This PEP proposes to change the default source encoding from ASCII to
|
||
UTF-8. Support for alternative source encodings (:pep:`263`) continues to
|
||
exist; an explicit encoding declaration takes precedence over the
|
||
default.
|
||
|
||
|
||
A Bit of History
|
||
================
|
||
|
||
In Python 1, the source encoding was unspecified, except that the
|
||
source encoding had to be a superset of the system's basic execution
|
||
character set (i.e. an ASCII superset, on most systems). The source
|
||
encoding was only relevant for the lexis itself (bytes representing
|
||
letters for keywords, identifiers, punctuation, line breaks, etc).
|
||
The contents of a string literal was copied literally from the file
|
||
on source.
|
||
|
||
In Python 2.0, the source encoding changed to Latin-1 as a side effect
|
||
of introducing Unicode. For Unicode string literals, the characters
|
||
were still copied literally from the source file, but widened on a
|
||
character-by-character basis. As Unicode gives a fixed interpretation
|
||
to code points, this algorithm effectively fixed a source encoding, at
|
||
least for files containing non-ASCII characters in Unicode literals.
|
||
|
||
:pep:`263` identified the problem that you can use only those Unicode
|
||
characters in a Unicode literal which are also in Latin-1, and
|
||
introduced a syntax for declaring the source encoding. If no source
|
||
encoding was given, the default should be ASCII. For compatibility
|
||
with Python 2.0 and 2.1, files were interpreted as Latin-1 for a
|
||
transitional period. This transition ended with Python 2.5, which
|
||
gives an error if non-ASCII characters are encountered and no source
|
||
encoding is declared.
|
||
|
||
Rationale
|
||
=========
|
||
|
||
With :pep:`263`, using arbitrary non-ASCII characters in a Python file is
|
||
possible, but tedious. One has to explicitly add an encoding
|
||
declaration. Even though some editors (like IDLE and Emacs) support
|
||
the declarations of :pep:`263`, many editors still do not (and never
|
||
will); users have to explicitly adjust the encoding which the editor
|
||
assumes on a file-by-file basis.
|
||
|
||
When the default encoding is changed to UTF-8, adding non-ASCII text
|
||
to Python files becomes easier and more portable: On some systems,
|
||
editors will automatically choose UTF-8 when saving text (e.g. on Unix
|
||
systems where the locale uses UTF-8). On other systems, editors will
|
||
guess the encoding when reading the file, and UTF-8 is easy to
|
||
guess. Yet other editors support associating a default encoding with a
|
||
file extension, allowing users to associate .py with UTF-8.
|
||
|
||
For Python 2, an important reason for using non-UTF-8 encodings was
|
||
that byte string literals would be in the source encoding at run-time,
|
||
allowing then to output them to a file or render them to the user
|
||
as-is. With Python 3, all strings will be Unicode strings, so the
|
||
original encoding of the source will have no impact at run-time.
|
||
|
||
Implementation
|
||
==============
|
||
|
||
The parser needs to be changed to accept bytes > 127 if no source
|
||
encoding is specified; instead of giving an error, it needs to check
|
||
that the bytes are well-formed UTF-8 (decoding is not necessary,
|
||
as the parser converts all source code to UTF-8, anyway).
|
||
|
||
IDLE needs to be changed to use UTF-8 as the default encoding.
|
||
|
||
|
||
Copyright
|
||
=========
|
||
|
||
This document has been placed in the public domain.
|
||
|
||
|
||
|
||
..
|
||
Local Variables:
|
||
mode: indented-text
|
||
indent-tabs-mode: nil
|
||
sentence-end-double-space: t
|
||
fill-column: 70
|
||
coding: utf-8
|
||
End:
|