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PEP 434 update from Todd.

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Georg Brandl 2013-03-29 09:10:34 +01:00
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@ -11,23 +11,24 @@ Content-Type: text/x-rst
Created: 16-Feb-2013
Post-History: 16-Feb-2013
03-Mar-2013
21-Mar-2013
Abstract
========
Most CPython tracker issues are classified as behavior or
enhancement. Most behavior patches are backported to branches for
existing versions. Enhancement patches are restricted to the default
branch that becomes the next Python version.
Most CPython tracker issues are classified as behavior or enhancement.
Most behavior patches are backported to branches for existing
versions. Enhancement patches are restricted to the default branch
that becomes the next Python version.
This PEP proposes that the restriction on applying enhancements be
relaxed for IDLE code, residing in .../Lib/idlelib/. In practice,
this would mean that IDLE developers would not have to classify or
agree on the classification of a patch but could instead focus on
what is best for IDLE users and future IDLE developement. It would
also mean that IDLE patches would not necessarily have to be split
into 'bugfix' changes and enhancement changes.
agree on the classification of a patch but could instead focus on what
is best for IDLE users and future IDLE development. It would also
mean that IDLE patches would not necessarily have to be split into
'bugfix' changes and enhancement changes.
The PEP would apply to changes in existing features and addition of
small features, such as would require a new menu entry, but not
@ -40,102 +41,115 @@ Motivation
This PEP was prompted by controversy on both the tracker and pydev
list over adding Cut, Copy, and Paste to right-click context menus
(Issue 1207589, opened in 2005 [1]_; pydev thread [2]_). The
features were available as keyboard shortcuts but not on the context
menu. It is standard, at least on Windows, that they should be when
applicable (a read-only window would only have Copy), so users do not
have to shift to the keyboard after selecting text for cutting or
copying or a slice point for pasting. The context menu was not
documented until 10 days before the new options were added (Issue
10405 [3]_).
(Issue 1207589, opened in 2005 [1]_; pydev thread [2]_). The features
were available as keyboard shortcuts but not on the context menu. It
is standard, at least on Windows, that they should be when applicable
(a read-only window would only have Copy), so users do not have to
shift to the keyboard after selecting text for cutting or copying or a
slice point for pasting. The context menu was not documented until 10
days before the new options were added (Issue 10405 [5]_).
Normally, behavior is called a bug if it conflicts with documentation
judged to be correct. But if there is no doc, what is the standard?
judged to be correct. But if there is no doc, what is the standard?
If the code is its own documentation, most IDLE issues on the tracker
are enhancement issues. If we substitute reasonable user expectation,
(which can, of course, be its own subject of disagreement), many more
issues are behavior issues.
For context menus, people disagreed on the status of the additions --
bugfix or enhancement. Even people who called it an enhancement
bugfix or enhancement. Even people who called it an enhancement
disagreed as to whether the patch should be backported. This PEP
proposes to make the status disagreement irrelevant by explicitly
allowing more liberal backporting than for other stdlib modules.
Python does have many advanced features yet Python is well known for
being a easy computer language for beginners [3]_. A major Python
philosophy is "batteries included" which is best demonstrated in
Python's standard library with many modules that are not typically
included with other programming languages [4]_. IDLE is a important
"battery" in the Python toolbox because it allows a beginner to get
started quickly without downloading and configuring a third party IDE.
IDLE represents a commitment by the Python community to encouage the
use of Python as a teaching language both inside and outside of formal
educational settings. The recommended teaching experience is to have
a learner start with IDLE. This PEP and the work that it will enable
will allow the Python community to make that learner's experience with
IDLE awesome by making IDLE a simple tool for beginners to get started
with Python.
Rationale
=========
People primarily use IDLE by running the gui application, rather than
by directly importing the effectively private (undocumented)
implementation modules in idlelib. Whether they use the shell, the
editor, or both, we believe they will benefit more from consistency
across the latest releases of current Python versions than from
consistency within the bugfix releases for one Python version. This
is especially true when existing behavior is clearly unsatisfactory.
People primarily use IDLE by running the graphical user interface
(GUI) application, rather than by directly importing the effectively
private (undocumented) implementation modules in idlelib. Whether
they use the shell, the editor, or both, we believe they will benefit
more from consistency across the latest releases of current Python
versions than from consistency within the bugfix releases for one
Python version. This is especially true when existing behavior is
clearly unsatisfactory.
When people use the standard interpreter, the OS-provided frame works
pretty much the same for all Python versions. If, for instance,
Microsoft were to upgrade the Command Prompt gui, the improvements
would be present regardless of which Python were running within it.
Similarly, if one edits Python code with editor X, behaviors such as
the right-click context menu and the search-replace box do not depend
on the version of Python being edited or even the language being
edited.
the same for all Python versions. If, for instance, Microsoft were to
upgrade the Command Prompt GUI, the improvements would be present
regardless of which Python were running within it. Similarly, if one
edits Python code with editor X, behaviors such as the right-click
context menu and the search-replace box do not depend on the version
of Python being edited or even the language being edited.
The benefit for IDLE developers is mixed. On the one hand, testing
The benefit for IDLE developers is mixed. On the one hand, testing
more versions and possibly having to adjust a patch, especially for
2.7, is more work. (There is, of course, the option on not
backporting everything. For issue 12510, some changes to calltips for
2.7, is more work. (There is, of course, the option on not
backporting everything. For issue 12510, some changes to calltips for
classes were not included in the 2.7 patch because of issues with
old-style classes [4]_.) On the other hand, bike-shedding can be an
energy drain. If the obvious fix for a bug looks like an enhancement,
writing a separate bugfix-only patch is more work. And making the
old-style classes [6]_.) On the other hand, bike-shedding can be an
energy drain. If the obvious fix for a bug looks like an enhancement,
writing a separate bugfix-only patch is more work. And making the
code diverge between versions makes future multi-version patches more
difficult.
These issue are illustrated by the search-and-replace dialog box.
It used to raise an exception for certain user entries [5]_. The
uncaught exception caused IDLE to exit. At least on Windows, the
exit was silent (no visible traceback) and looked like a crash if
IDLE was started normally, from an icon.
These issue are illustrated by the search-and-replace dialog box. It
used to raise an exception for certain user entries [7]_. The
uncaught exception caused IDLE to exit. At least on Windows, the exit
was silent (no visible traceback) and looked like a crash if IDLE was
started normally, from an icon.
Was this a bug? IDLE Help (on the current Help submenu) just says
"Replace... Open a search-and-replace dialog box", and a box *was*
opened. It is not, in general, a bug for a library method to raise an
"Replace... Open a search-and-replace dialog box", and a box *was*
opened. It is not, in general, a bug for a library method to raise an
exception. And it is not, in general, a bug for a library method to
ignore an exception raised by functions it calls. So if we were to
adopt the 'code = doc' philosopy in the absence of detailed docs, one
ignore an exception raised by functions it calls. So if we were to
adopt the 'code = doc' philosophy in the absence of detailed docs, one
might say 'No'.
However, IDLE exiting when it does not need to is definitely
obnoxious. So four of us agreed that it should be prevented. But
obnoxious. So four of us agreed that it should be prevented. But
there was still the question of what to do instead? Catch the
exception? Just not raise the exception? Beep? Display an error
message box? Or try to do something useful with the user's entry?
Would replacing a 'crash' with useful behavior be an enhancement,
limited to future Python releases? Should IDLE developers have to
ask that?
limited to future Python releases? Should IDLE developers have to ask
that?
Backwards Compatibility
=======================
For IDLE, there are three types of users who might be concerned about
back compatibility. First are people who run IDLE as an application.
back compatibility. First are people who run IDLE as an application.
We have already discussed them above.
Second are people who import one of the idlelib modules. As far as
we know, this is only done to start the IDLE application, and we do
not propose breaking such use. Otherwise, the modules are
undocumented and effectively private implementations. If an IDLE
module were defined as public, documented, and perhaps moved to the
tkinter package, it would then follow the normal rules. (Documenting
the private interfaces for the benefit of people working on the IDLE
code is a separate issue.)
Second are people who import one of the idlelib modules. As far as we
know, this is only done to start the IDLE application, and we do not
propose breaking such use. Otherwise, the modules are undocumented
and effectively private implementations. If an IDLE module were
defined as public, documented, and perhaps moved to the tkinter
package, it would then follow the normal rules. (Documenting the
private interfaces for the benefit of people working on the IDLE code
is a separate issue.)
Third are people who write IDLE extensions. The guaranteed extension
interface is given in idlelib/extension.txt. This should be respected
Third are people who write IDLE extensions. The guaranteed extension
interface is given in idlelib/extension.txt. This should be respected
at least in existing versions, and not frivolously changed in future
versions. But there is a warning that "The extension cannot assume
much about this [EditorWindow] argument." This guarantee should
@ -150,7 +164,6 @@ whether this violates the guarantee, but there is a second patch that
fixes assumption b). It should be applied when it is clear that the
first patch will not have to be reverted.
References
==========
@ -160,14 +173,19 @@ References
.. [2] Cut/Copy/Paste items in IDLE right click context menu
(http://mail.python.org/pipermail/python-dev/2012-November/122514.html)
.. [3] IDLE breakpoint facility undocumented, Daily, Ned
.. [3] Getting Started with Python
(http://www.python.org/about/gettingstarted/)
.. [4] Batteries Included
(http://docs.python.org/2/tutorial/stdlib.html#batteries-included)
.. [5] IDLE breakpoint facility undocumented, Deily, Ned
(http://bugs.python.org/issue10405)
.. [4] IDLE: calltips mishandle raw strings and other examples,
Reedy, Terry
(http://bugs.python.org/issue12510)
.. [6] IDLE: calltips mishandle raw strings and other examples,
Reedy, Terry (http://bugs.python.org/issue12510)
.. [5] IDLE: replace ending with '\' causes crash, Reedy, Terry
.. [7] IDLE: replace ending with '\' causes crash, Reedy, Terry
(http://bugs.python.org/issue13052)