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2 changes: 1 addition & 1 deletion pep-0001.txt
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Expand Up @@ -68,7 +68,7 @@ PEP Workflow
Python's BDFL
-------------

There are several reference in this PEP to the "BDFL". This acronym stands
There are several references in this PEP to the "BDFL". This acronym stands
for "Benevolent Dictator for Life" and refers to Guido van Rossum, the
original creator of, and the final design authority for, the Python
programming language.
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82 changes: 44 additions & 38 deletions pep-0160.txt
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Expand Up @@ -5,73 +5,79 @@ Last-Modified: $Date$
Author: Fred L. Drake, Jr. <[email protected]>
Status: Final
Type: Informational
Content-Type: text/x-rst
Created: 25-Jul-2000
Python-Version: 1.6
Post-History:


Introduction
============

This PEP describes the Python 1.6 release schedule. The CVS
revision history of this file contains the definitive historical
record.
This PEP describes the Python 1.6 release schedule. The CVS
revision history of this file contains the definitive historical
record.

This release will be produced by BeOpen PythonLabs staff for the
Corporation for National Research Initiatives (CNRI).
This release will be produced by BeOpen PythonLabs staff for the
Corporation for National Research Initiatives (CNRI).


Schedule
========

August 1 1.6 beta 1 release (planned).
August 3 1.6 beta 1 release (actual).
August 15 1.6 final release (planned).
September 5 1.6 final release (actual).
* August 1: 1.6 beta 1 release (planned).
* August 3: 1.6 beta 1 release (actual).
* August 15: 1.6 final release (planned).
* September 5: 1.6 final release (actual).


Features
========

A number of features are required for Python 1.6 in order to
fulfill the various promises that have been made. The following
are required to be fully operational, documented, and forward
compatible with the plans for Python 2.0:
A number of features are required for Python 1.6 in order to
fulfill the various promises that have been made. The following
are required to be fully operational, documented, and forward
compatible with the plans for Python 2.0:

* Unicode support: The Unicode object defined for Python 2.0 must
be provided, including all methods and codec support.
* Unicode support: The Unicode object defined for Python 2.0 must be provided,
including all methods and codec support.

* SRE: Fredrik Lundh's new regular expression engine will be used
to provide support for both 8-bit strings and Unicode strings.
It must pass the regression test used for the pcre-based version
of the re module.
* SRE: Fredrik Lundh's new regular expression engine will be used
to provide support for both 8-bit strings and Unicode strings. It must pass
the regression test used for the pcre-based version of the re module.

* The curses module was in the middle of a transformation to a
package, so the final form was adopted.
* The curses module was in the middle of a transformation to a package, so the
final form was adopted.


Mechanism
=========

The release will be created as a branch from the development tree
rooted at CNRI's close of business on 16 May 2000. Patches
required from more recent checkins will be merged in by moving the
branch tag on individual files whenever possible in order to
reduce mailing list clutter and avoid divergent and incompatible
implementations.
The release will be created as a branch from the development tree
rooted at CNRI's close of business on 16 May 2000. Patches
required from more recent checkins will be merged in by moving the
branch tag on individual files whenever possible in order to
reduce mailing list clutter and avoid divergent and incompatible
implementations.

The branch tag is "cnri-16-start".
The branch tag is "cnri-16-start".

Patches and features will be merged to the extent required to pass
regression tests in effect on 16 May 2000.
Patches and features will be merged to the extent required to pass
regression tests in effect on 16 May 2000.

The beta release is tagged "r16b1" in the CVS repository, and the
final Python 1.6 release is tagged "release16" in the repository.
The beta release is tagged "r16b1" in the CVS repository, and the
final Python 1.6 release is tagged "release16" in the repository.


Copyright
=========

This document has been placed in the public domain.
This document has been placed in the public domain.



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12 changes: 7 additions & 5 deletions pep-0210.txt
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Expand Up @@ -5,13 +5,15 @@ Last-Modified: $Date$
Author: [email protected] (David Ascher)
Status: Rejected
Type: Standards Track
Content-Type: text/x-rst
Created: 15-Jul-2000
Python-Version: 2.1
Post-History:



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197 changes: 106 additions & 91 deletions pep-0215.txt
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Expand Up @@ -5,139 +5,154 @@ Last-Modified: $Date$
Author: [email protected] (Ka-Ping Yee)
Status: Superseded
Type: Standards Track
Content-Type: text/x-rst
Created: 24-Jul-2000
Python-Version: 2.1
Post-History:
Superseded-By: 292


Abstract
========

This document proposes a string interpolation feature for Python
to allow easier string formatting. The suggested syntax change
is the introduction of a '$' prefix that triggers the special
interpretation of the '$' character within a string, in a manner
reminiscent to the variable interpolation found in Unix shells,
awk, Perl, or Tcl.
This document proposes a string interpolation feature for Python
to allow easier string formatting. The suggested syntax change
is the introduction of a '$' prefix that triggers the special
interpretation of the '$' character within a string, in a manner
reminiscent to the variable interpolation found in Unix shells,
awk, Perl, or Tcl.


Copyright
=========

This document is in the public domain.
This document is in the public domain.


Specification
=============

Strings may be preceded with a '$' prefix that comes before the
leading single or double quotation mark (or triplet) and before
any of the other string prefixes ('r' or 'u'). Such a string is
processed for interpolation after the normal interpretation of
backslash-escapes in its contents. The processing occurs just
before the string is pushed onto the value stack, each time the
string is pushed. In short, Python behaves exactly as if '$'
were a unary operator applied to the string. The operation
performed is as follows:
Strings may be preceded with a '$' prefix that comes before the
leading single or double quotation mark (or triplet) and before
any of the other string prefixes ('r' or 'u'). Such a string is
processed for interpolation after the normal interpretation of
backslash-escapes in its contents. The processing occurs just
before the string is pushed onto the value stack, each time the
string is pushed. In short, Python behaves exactly as if '$'
were a unary operator applied to the string. The operation
performed is as follows:

The string is scanned from start to end for the '$' character
(\x24 in 8-bit strings or \u0024 in Unicode strings). If there
are no '$' characters present, the string is returned unchanged.
The string is scanned from start to end for the '$' character
(``\x24`` in 8-bit strings or ``\u0024`` in Unicode strings). If there
are no '$' characters present, the string is returned unchanged.

Any '$' found in the string, followed by one of the two kinds of
expressions described below, is replaced with the value of the
expression as evaluated in the current namespaces. The value is
converted with str() if the containing string is an 8-bit string,
or with unicode() if it is a Unicode string.
Any '$' found in the string, followed by one of the two kinds of
expressions described below, is replaced with the value of the
expression as evaluated in the current namespaces. The value is
converted with ``str()`` if the containing string is an 8-bit string,
or with ``unicode()`` if it is a Unicode string.

1. A Python identifier optionally followed by any number of
trailers, where a trailer consists of:
- a dot and an identifier,
- an expression enclosed in square brackets, or
- an argument list enclosed in parentheses
(This is exactly the pattern expressed in the Python grammar
by "NAME trailer*", using the definitions in Grammar/Grammar.)
1. A Python identifier optionally followed by any number of
trailers, where a trailer consists of:
- a dot and an identifier,
- an expression enclosed in square brackets, or
- an argument list enclosed in parentheses
(This is exactly the pattern expressed in the Python grammar
by "``NAME`` trailer*", using the definitions in Grammar/Grammar.)

2. Any complete Python expression enclosed in curly braces.
2. Any complete Python expression enclosed in curly braces.

Two dollar-signs ("$$") are replaced with a single "$".
Two dollar-signs ("$$") are replaced with a single "$".


Examples

Here is an example of an interactive session exhibiting the
expected behaviour of this feature.

>>> a, b = 5, 6
>>> print $'a = $a, b = $b'
a = 5, b = 6
>>> $u'uni${a}ode'
u'uni5ode'
>>> print $'\$a'
5
>>> print $r'\$a'
\5
>>> print $'$$$a.$b'
$5.6
>>> print $'a + b = ${a + b}'
a + b = 11
>>> import sys
>>> print $'References to $a: $sys.getrefcount(a)'
References to 5: 15
>>> print $"sys = $sys, sys = $sys.modules['sys']"
sys = <module 'sys' (built-in)>, sys = <module 'sys' (built-in)>
>>> print $'BDFL = $sys.copyright.split()[4].upper()'
BDFL = GUIDO
========

Here is an example of an interactive session exhibiting the
expected behaviour of this feature::

>>> a, b = 5, 6
>>> print $'a = $a, b = $b'
a = 5, b = 6
>>> $u'uni${a}ode'
u'uni5ode'
>>> print $'\$a'
5
>>> print $r'\$a'
\5
>>> print $'$$$a.$b'
$5.6
>>> print $'a + b = ${a + b}'
a + b = 11
>>> import sys
>>> print $'References to $a: $sys.getrefcount(a)'
References to 5: 15
>>> print $"sys = $sys, sys = $sys.modules['sys']"
sys = <module 'sys' (built-in)>, sys = <module 'sys' (built-in)>
>>> print $'BDFL = $sys.copyright.split()[4].upper()'
BDFL = GUIDO


Discussion
==========

'$' is chosen as the interpolation character within the
string for the sake of familiarity, since it is already used
for this purpose in many other languages and contexts.
'$' is chosen as the interpolation character within the
string for the sake of familiarity, since it is already used
for this purpose in many other languages and contexts.

It is then natural to choose '$' as a prefix, since it is a
mnemonic for the interpolation character.
It is then natural to choose '$' as a prefix, since it is a
mnemonic for the interpolation character.

Trailers are permitted to give this interpolation mechanism
even more power than the interpolation available in most other
languages, while the expression to be interpolated remains
clearly visible and free of curly braces.
Trailers are permitted to give this interpolation mechanism
even more power than the interpolation available in most other
languages, while the expression to be interpolated remains
clearly visible and free of curly braces.

'$' works like an operator and could be implemented as an
operator, but that prevents the compile-time optimization
and presents security issues. So, it is only allowed as a
string prefix.
'$' works like an operator and could be implemented as an
operator, but that prevents the compile-time optimization
and presents security issues. So, it is only allowed as a
string prefix.


Security Issues
===============

"$" has the power to eval, but only to eval a literal. As
described here (a string prefix rather than an operator), it
introduces no new security issues since the expressions to be
evaluated must be literally present in the code.
"$" has the power to eval, but only to eval a literal. As
described here (a string prefix rather than an operator), it
introduces no new security issues since the expressions to be
evaluated must be literally present in the code.


Implementation
==============

The ``Itpl`` module at [1]_ provides a
prototype of this feature. It uses the tokenize module to find
the end of an expression to be interpolated, then calls ``eval()``
on the expression each time a value is needed. In the prototype,
the expression is parsed and compiled again each time it is
evaluated.

As an optimization, interpolated strings could be compiled
directly into the corresponding bytecode; that is::

$'a = $a, b = $b'

The Itpl module at http://www.lfw.org/python/Itpl.py provides a
prototype of this feature. It uses the tokenize module to find
the end of an expression to be interpolated, then calls eval()
on the expression each time a value is needed. In the prototype,
the expression is parsed and compiled again each time it is
evaluated.
could be compiled as though it were the expression::

As an optimization, interpolated strings could be compiled
directly into the corresponding bytecode; that is,
('a = ' + str(a) + ', b = ' + str(b))

$'a = $a, b = $b'
so that it only needs to be compiled once.

could be compiled as though it were the expression

('a = ' + str(a) + ', b = ' + str(b))
References
==========

so that it only needs to be compiled once.
.. [1] http://www.lfw.org/python/Itpl.py


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