#LyX 1.3 created this file. For more info see http://www.lyx.org/
\lyxformat 221
\textclass article
\begin_preamble
\usepackage{ae,aecompl}
\usepackage{hyperref}
\usepackage{html}
\end_preamble
\language english
\inputencoding auto
\fontscheme default
\graphics default
\paperfontsize default
\spacing single 
\papersize Default
\paperpackage a4
\use_geometry 1
\use_amsmath 0
\use_natbib 0
\use_numerical_citations 0
\paperorientation portrait
\leftmargin 1.25in
\topmargin 1in
\rightmargin 1.25in
\bottommargin 1in
\secnumdepth 3
\tocdepth 3
\paragraph_separation skip
\defskip medskip
\quotes_language english
\quotes_times 2
\papercolumns 1
\papersides 1
\paperpagestyle default

\layout Title

IPython
\newline 

\size larger 
New design notes
\layout Author

Fernando Pérez
\layout Section

Introduction
\layout Standard

This is a draft document with notes and ideas for the IPython rewrite.
 The section order and structure of this document roughly reflects in which
 order things should be done and what the dependencies are.
 This document is mainly a draft for developers, a pdf version is provided
 with the standard distribution in case regular users are interested and
 wish to contribute ideas.
\layout Standard

A tentative plan for the future:
\layout Itemize

0.6.x series: in practice, enough people are using IPython for real work that
 I think it warrants a higher number.
 This series will continue to evolve with bugfixes and incremental improvements.
\layout Itemize

0.7.x series: (maybe) If resources allow, there may be a branch for 'unstable'
 development, where the architectural rewrite may take place.
\layout Standard

However, I am starting to doubt it is feasible to keep two separate branches.
 I am leaning more towards a 
\begin_inset ERT
status Collapsed

\layout Standard

\backslash 
LyX
\end_inset 

-like approach, where the main branch slowly transforms and evolves.
 Having CVS support now makes this a reasonable alternative, as I don't
 have to make pre-releases as often.
 The active branch can remain the mainline of development, and users interested
 in the bleeding-edge stuff can always grab the CVS code.
\layout Standard

Ideally, IPython should have a clean class setup that would allow further
 extensions for special-purpose systems.
 I view IPython as a base system that provides a great interactive environment
 with full access to the Python language, and which could be used in many
 different contexts.
 The basic hooks are there: the magic extension syntax and the flexible
 system of recursive configuration files and profiles.
 But with a code as messy as the current one, nobody is going to touch it.
\layout Section

Immediate TODO and bug list
\layout Standard

Things that should be done for the current series, before starting major
 changes.
\layout Itemize

Fix any bugs reported at the online bug tracker.
\layout Itemize

History bug: I often see that, under certain circumstances, the input history
 is incorrect.
 The problem is that so far, I've failed to find a simple way to reproduce
 it consistently, so I can't easily track it down.
 It seems to me that it happens when output is generated multiple times
 for the same input (for i in range(10): i will do it).
 But even this isn't reliable...
 Ultimately the right solution for this is to cleanly separate the dataflow
 for input/output history management; right now that happens all over the
 place, which makes the code impossible to debug, and almost guaranteed
 to be buggy in the first place.
\layout Itemize


\series bold 
Redesign the output traps.

\series default 
 They cause problems when users try to execute code which relies on sys.stdout
 being the 'true' sys.stdout.
 They also prevent scripts which use raw_input() to work as command-line
 arguments.
\newline 
The best solution is probably to print the banner first, and then just execute
 all the user code straight with no output traps at all.
 Whatever comes out comes out.
 This makes the ipython code actually simpler, and eliminates the problem
 altogether.
\newline 
These things need to be ripped out, they cause no end of problems.
 For example, if user code requires acces to stdin during startup, the process
 just hangs indefinitely.
 For now I've just disabled them, and I'll live with the ugly error messages.
\layout Itemize

The prompt specials dictionary should be turned into a class which does
 proper namespace management, since the prompt specials need to be evaluated
 in a certain namespace.
 Currently it's just globals, which need to be managed manually by code
 below.
 
\layout Itemize

Fix coloring of prompts: the pysh color strings don't have any effect on
 prompt numbers, b/c these are controlled by the global scheme.
 Make the prompts fully user-definable, colors and all.
 This is what I said to a user:
\newline 
As far as the green 
\backslash 
#, this is a minor bug of the coloring code due to the vagaries of history.
 While the color strings allow you to control the coloring of most elements,
 there are a few which are still controlled by the old ipython internal
 coloring code, which only accepts a global 'color scheme' choice.
 So basically the input/output numbers are hardwired to the choice in the
 color scheme, and there are only 'Linux', 'LightBG' and 'NoColor' schemes
 to choose from.
 
\layout Itemize

Clean up FakeModule issues.
 Currently, unittesting with embedded ipython breaks because a FakeModule
 instance overwrites __main__.
 Maybe ipython should revert back to using __main__ directly as the user
 namespace? Handling a separate namespace is proving 
\emph on 
very
\emph default 
 tricky in all corner cases.
\layout Itemize

Make the output cache depth independent of the input one.
 This way one can have say only the last 10 results stored and still have
 a long input history/cache.
\layout Itemize

Fix the fact that importing a shell for embedding screws up the command-line
 history.
 This can be done by not importing the history file when the shell is already
 inside ipython.
\layout Itemize

Lay out the class structure so that embedding into a gtk/wx/qt app is trivial,
 much like the multithreaded gui shells now provide command-line coexistence
 with the gui toolkits.
 See 
\begin_inset LatexCommand \url{http://www.livejournal.com/users/glyf/32396.html}

\end_inset 


\layout Itemize

Get Holger's completer in, once he adds filename completion.
\layout Standard

Lower priority stuff:
\layout Itemize

Add @showopt/@setopt (decide name) for viewing/setting all options.
 The existing option-setting magics should become aliases for setopt calls.
\layout Itemize

It would be nice to be able to continue with python stuff after an @ command.
 For instance "@run something; test_stuff()" in order to test stuff even
 faster.
 Suggestion by Kasper Souren <Kasper.Souren@ircam.fr>
\layout Itemize

Run a 'first time wizard' which configures a few things for the user, such
 as color_info, editor and the like.
\layout Itemize

Logging: @logstart and -log should start logfiles in ~.ipython, but with
 unique names in case of collisions.
 This would prevent ipython.log files all over while also allowing multiple
 sessions.
 Also the -log option should take an optional filename, instead of having
 a separate -logfile option.
\newline 
In general the logging system needs a serious cleanup.
 Many functions now in Magic should be moved to Logger, and the magic @s
 should be very simple wrappers to the Logger methods.
\layout Section

Lighten the code
\layout Standard

If we decide to base future versions of IPython on Python 2.3, which has
 the new Optik module (called optparse), it should be possible to drop DPyGetOpt.
 We should also remove the need for Itpl.
 Another area for trimming is the Gnuplot stuff: much of that could be merged
 into the mainline project.
\layout Standard

Double check whether we really need FlexCompleter.
 This was written as an enhanced rlcompleter, but my patches went in for
 python 2.2 (or 2.3, can't remember).
\layout Standard

With these changes we could shed a fair bit of code from the main trunk.
\layout Section

Unit testing
\layout Standard

All new code should use a testing framework.
 Python seems to have very good testing facilities, I just need to learn
 how to use them.
 I should also check out QMTest at 
\begin_inset LatexCommand \htmlurl{http://www.codesourcery.com/qm/qmtest}

\end_inset 

, it sounds interesting (it's Python-based too).
\layout Section

Configuration system
\layout Standard

Move away from the current ipythonrc format to using standard python files
 for configuration.
 This will require users to be slightly more careful in their syntax, but
 reduces code in IPython, is more in line with Python's normal form (using
 the $PYTHONSTARTUP file) and allows much more flexibility.
 I also think it's more 'pythonic', in using a single language for everything.
\layout Standard

Options can be set up with a function call which takes keywords and updates
 the options Struct.
\layout Standard

In order to maintain the recursive inclusion system, write an 'include'
 function which is basically a wrapper around safe_execfile().
 Also for alias definitions an alias() function will do.
 All functionality which we want to have at startup time for the users can
 be wrapped in a small module so that config files look like:
\layout Standard


\family typewriter 
from IPython.Startup import *
\newline 
...
\newline 
set_options(automagic=1,colors='NoColor',...)
\newline 
...
\newline 
include('mysetup.py')
\newline 
...
\newline 
alias('ls ls --color -l')
\newline 
...
 etc.
\layout Standard

Also, put 
\series bold 
all
\series default 
 aliases in here, out of the core code.
\layout Standard

The new system should allow for more seamless upgrading, so that:
\layout Itemize

It automatically recognizes when the config files need updating and does
 the upgrade.
\layout Itemize

It simply adds the new options to the user's config file without overwriting
 it.
 The current system is annoying since users need to manually re-sync their
 configuration after every update.
\layout Itemize

It detects obsolete options and informs the user to remove them from his
 config file.
\layout Standard

Here's a copy of Arnd Baecker suggestions on the matter:
\layout Standard

1.) upgrade: it might be nice to have an "auto" upgrade procedure: i.e.
 imagine that IPython is installed system-wide and gets upgraded, how does
 a user know, that an upgrade of the stuff in ~/.ipython is necessary ? So
 maybe one has to a keep a version number in ~/.ipython and if there is a
 mismatch with the started ipython, then invoke the upgrade procedure.
\layout Standard

2.) upgrade: I find that replacing the old files in ~/.ipython (after copying
 them to .old not optimal (for example, after every update, I have to change
 my color settings (and some others) in ~/.ipython/ipthonrc).
 So somehow keeping the old files and merging the new features would be
 nice.
 (but how to distinguish changes from version to version with changes made
 by the user ?) For, example, I would have to change in GnuplotMagic.py gnuplot_m
ouse to 1 after every upgrade ...
\layout Standard

This is surely a minor point - also things will change during the "BIG"
 rewrite, but maybe this is a point to keep in mind for this ?
\layout Standard

3.) upgrade: old, sometimes obsolete files stay in the ~/.ipython subdirectory.
 (hmm, maybe one could move all these into some subdirectory, but which
 name for that (via version-number ?) ?)
\layout Subsection

Command line options
\layout Standard

It would be great to design the command-line processing system so that it
 can be dynamically modified in some easy way.
 This would allow systems based on IPython to include their own command-line
 processing to either extend or fully replace IPython's.
 Probably moving to the new optparse library (also known as optik) will
 make this a lot easier.
\layout Section

OS-dependent code
\layout Standard

Options which are OS-dependent (such as colors and aliases) should be loaded
 via include files.
 That is, the general file will have:
\layout Standard


\family typewriter 
if os.name == 'posix':
\newline 
include('ipythonrc-posix.py')
\newline 
elif os.name == 'nt':
\newline 
include('ipythonrc-nt.py')...
\layout Standard

In the 
\family typewriter 
-posix
\family default 
, 
\family typewriter 
-nt
\family default 
, etc.
 files we'll set all os-specific options.
\layout Section

Merging with other shell systems
\layout Standard

This is listed before the big design issues, as it is something which should
 be kept in mind when that design is made.
\layout Standard

The following shell systems are out there and I think the whole design of
 IPython should try to be modular enough to make it possible to integrate
 its features into these.
 In all cases IPython should exist as a stand-alone, terminal based program.
 But it would be great if users of these other shells (some of them which
 have very nice features of their own, especially the graphical ones) could
 keep their environment but gain IPython's features.
\layout List
\labelwidthstring 00.00.0000

IDLE This is the standard, distributed as part of Python.
 
\layout List
\labelwidthstring 00.00.0000

pyrepl 
\begin_inset LatexCommand \htmlurl{http://starship.python.net/crew/mwh/hacks/pyrepl.html}

\end_inset 

.
 This is a text (curses-based) shell-like replacement which doesn't have
 some of IPython's features, but has a crucially useful (and hard to implement)
 one: full multi-line editing.
 This turns the interactive interpreter into a true code testing and development
 environment.
 
\layout List
\labelwidthstring 00.00.0000

PyCrust 
\begin_inset LatexCommand \htmlurl{http://sourceforge.net/projects/pycrust}

\end_inset 

.
 Very nice, wxWindows based system.
\layout List
\labelwidthstring 00.00.0000

PythonWin 
\begin_inset LatexCommand \htmlurl{http://starship.python.net/crew/mhammond}

\end_inset 

.
 Similar to PyCrust in some respects, a very good and free Python development
 environment for Windows systems.
\layout Section

Class design
\layout Standard

This is the big one.
 Currently classes use each other in a very messy way, poking inside one
 another for data and methods.
 ipmaker() adds tons of stuff to the main __IP instance by hand, and the
 mix-ins used (Logger, Magic, etc) mean the final __IP instance has a million
 things in it.
 All that needs to be cleanly broken down with well defined interfaces amongst
 the different classes, and probably no mix-ins.
\layout Standard

The best approach is probably to have all the sub-systems which are currently
 mixins be fully independent classes which talk back only to the main instance
 (and 
\series bold 
not
\series default 
 to each other).
 In the main instance there should be an object whose job is to handle communica
tion with the sub-systems.
\layout Standard

I should probably learn a little UML and diagram this whole thing before
 I start coding.
\layout Subsection

Magic
\layout Standard

Now all methods which will become publicly available are called Magic.magic_name,
 the magic_ should go away.
 Then, Magic instead of being a mix-in should simply be an attribute of
 __IP:
\layout Standard

__IP.Magic = Magic()
\layout Standard

This will then give all the magic functions as __IP.Magic.name(), which is
 much cleaner.
 This will also force a better separation so that Magic doesn't poke inside
 __IP so much.
 In the constructor, Magic should get whatever information it needs to know
 about __IP (even if it means a pointer to __IP itself, but at least we'll
 know where it is.
 Right now since it's a mix-in, there's no way to know which variables belong
 to whom).
\layout Standard

Build a class MagicFunction so that adding new functions is a matter of:
\layout Standard


\family typewriter 
my_magic = MagicFunction(category = 'System utilities')
\newline 
my_magic.__call__ = ...
\layout Standard

Features:
\layout Itemize

The class constructor should automatically register the functions and keep
 a table with category sections for easy sorting/viewing.
\layout Itemize

The object interface must allow automatic building of a GUI for them.
 This requires registering the options the command takes, the number of
 arguments, etc, in a formal way.
 The advantage of this approach is that it allows not only to add GUIs to
 the magics, but also for a much more intelligent building of docstrings,
 and better parsing of options and arguments.
\layout Standard

Also think through better an alias system for magics.
 Since the magic system is like a command shell inside ipython, the relation
 between these aliases and system aliases should be cleanly thought out.
\layout Subsection

Color schemes
\layout Standard

These should be loaded from some kind of resource file so they are easier
 to modify by the user.
\layout Section

Hooks
\layout Standard

IPython should have a modular system where functions can register themselves
 for certain tasks.
 Currently changing functionality requires overriding certain specific methods,
 there should be a clean API for this to be done.
\layout Subsection

whos hook
\layout Standard

This was a very nice suggestion from Alexander Schmolck <a.schmolck@gmx.net>:
\layout Standard

2.
 I think it would also be very helpful if there where some sort of hook
 for ``whos`` that let one customize display formaters depending on the
 object type.
\layout Standard

For example I'd rather have a whos that formats an array like:
\layout Standard


\family typewriter 
Variable Type Data/Length
\newline 
------------------------------ 
\newline 
a array size: 4x3 type: 'Float'
\layout Standard

than
\layout Standard


\family typewriter 
Variable Type Data/Length 
\newline 
------------------------------
\newline 
a array [[ 0.
 1.
 2.
 3<...> 8.
 9.
 10.
 11.]]
\layout Section

Parallel support
\layout Standard

For integration with graphical shells and other systems, it will be best
 if ipython is split into a kernel/client model, much like Mathematica works.
 This simultaneously opens the door for support of interactive parallel
 computing.
 Currenlty %bg provides a threads-based proof of concept, and Brian Granger's
 XGrid project is a much more realistic such system.
 The new design should integrates ideas as core elements.
 Some notes from Brian on this topic:
\layout Standard

1.
 How should the remote python server/kernel be designed? Multithreaded?
 Blocking? Connected/disconnected modes? Load balancing?
\layout Standard

2.
 What APi/protocol should the server/kernel expose to clients?
\layout Standard

3.
 How should the client classes (which the user uses to interact with the
 cluster) be designed?
\layout Standard

4.
 What API should the client classes expose?
\layout Standard

5.
 How should the client API be wrapped in a few simple magic functions?
\layout Standard

6.
 How should security be handled?
\layout Standard

7.
 How to work around the issues of the GIL and threads?
\layout Standard

I think the most important things to work out are the client API (#4) the
 server/kernel API/protocol (#2) and the magic function API (#5).
 We should let these determine the design and architecture of the components.
\layout Standard

One other thing.
 What is your impression of twisted? I have been looking at it and it looks
 like a _very_ powerful set of tools for this type of stuff.
 I am wondering if it might make sense to think about using twisted for
 this project.
\layout Section

Manuals
\layout Standard

The documentation should be generated from docstrings for the command line
 args and all the magic commands.
 Look into one of the simple text markup systems to see if we can get latex
 (for reLyXing later) out of this.
 Part of the build command would then be to make an update of the docs based
 on this, thus giving more complete manual (and guaranteed to be in sync
 with the code docstrings).
\layout Standard

[PARTLY DONE] At least now all magics are auto-documented, works farily
 well.
 Limited Latex formatting yet.
\layout Subsection

Integration with pydoc-help
\layout Standard

It should be possible to have access to the manual via the pydoc help system
 somehow.
 This might require subclassing the pydoc help, or figuring out how to add
 the IPython docs in the right form so that help() finds them.
\layout Standard

Some comments from Arnd and my reply on this topic:
\layout Standard

> ((Generally I would like to have the nice documentation > more easily
 accessable from within ipython ...
 > Many people just don't read documentation, even if it is > as good as
 the one of IPython ))
\layout Standard

That's an excellent point.
 I've added a note to this effect in new_design.
 Basically I'd like help() to naturally access the IPython docs.
 Since they are already there in html for the user, it's probably a matter
 of playing a bit with pydoc to tell it where to find them.
 It would definitely make for a much cleaner system.
 Right now the information on IPython is:
\layout Standard

-ipython --help at the command line: info on command line switches 
\layout Standard

-? at the ipython prompt: overview of IPython 
\layout Standard

-magic at the ipython prompt: overview of the magic system 
\layout Standard

-external docs (html/pdf)
\layout Standard

All that should be better integrated seamlessly in the help() system, so
 that you can simply say:
\layout Standard

help ipython -> full documentation access 
\layout Standard

help magic -> magic overview 
\layout Standard

help profile -> help on current profile 
\layout Standard

help -> normal python help access.
\layout Section

Graphical object browsers
\layout Standard

I'd like a system for graphically browsing through objects.
 
\family typewriter 
@obrowse
\family default 
 should open a widged with all the things which 
\family typewriter 
@who
\family default 
 lists, but cliking on each object would open a dedicated object viewer
 (also accessible as 
\family typewriter 
@oview <object>
\family default 
).
 This object viewer could show a summary of what 
\family typewriter 
<object>?
\family default 
 currently shows, but also colorize source code and show it via an html
 browser, show all attributes and methods of a given object (themselves
 openable in their own viewers, since in Python everything is an object),
 links to the parent classes, etc.
\layout Standard

The object viewer widget should be extensible, so that one can add methods
 to view certain types of objects in a special way (for example, plotting
 Numeric arrays via grace or gnuplot).
 This would be very useful when using IPython as part of an interactive
 complex system for working with certain types of data.
\layout Standard

I should look at what PyCrust has to offer along these lines, at least as
 a starting point.
\layout Section

Miscellaneous small things
\layout Itemize

Collect whatever variables matter from the environment in some globals for
 __IP, so we're not testing for them constantly (like $HOME, $TERM, etc.)
\layout Section

Session restoring
\layout Standard

I've convinced myself that session restore by log replay is too fragile
 and tricky to ever work reliably.
 Plus it can be dog slow.
 I'd rather have a way of saving/restoring the *current* memory state of
 IPython.
 I tried with pickle but failed (can't pickle modules).
 This seems the right way to do it to me, but it will have to wait until
 someone tells me of a robust way of dumping/reloading *all* of the user
 namespace in a file.
\layout Standard

Probably the best approach will be to pickle as much as possible and record
 what can not be pickled for manual reload (such as modules).
 This is not trivial to get to work reliably, so it's best left for after
 the code restructuring.
\layout Standard

The following issues exist (old notes, see above paragraph for my current
 take on the issue):
\layout Itemize

magic lines aren't properly re-executed when a log file is reloaded (and
 some of them, like clear or run, may change the environment).
 So session restore isn't 100% perfect.
\layout Itemize

auto-quote/parens lines aren't replayed either.
 All this could be done, but it needs some work.
 Basically it requires re-running the log through IPython itself, not through
 python.
\layout Itemize

_p variables aren't restored with a session.
 Fix: same as above.
\layout Section

Tips system
\layout Standard

It would be nice to have a tip() function which gives tips to users in some
 situations, but keeps track of already-given tips so they aren't given
 every time.
 This could be done by pickling a dict of given tips to IPYTHONDIR.
\layout Section

TAB completer
\layout Standard

Some suggestions from Arnd Baecker:
\layout Standard

a) For file related commands (ls, cat, ...) it would be nice to be able to
 TAB complete the files in the current directory.
 (once you started typing something which is uniquely a file, this leads
 to this effect, apart from going through the list of possible completions
 ...).
 (I know that this point is in your documentation.)
\layout Standard

More general, this might lead to something like command specific completion
 ? 
\layout Standard

Here's John Hunter's suggestion:
\layout Standard

The *right way to do it* would be to make intelligent or customizable choices
 about which namespace to add to the completion list depending on the string
 match up to the prompt, eg programmed completions.
 In the simplest implementation, one would only complete on files and directorie
s if the line preceding the tab press matched 'cd ' or 'run ' (eg you don't
 want callable showing up in 'cd ca<TAB>')
\layout Standard

In a more advanced scenario, you might imaging that functions supplied the
 TAB namespace, and the user could configure a dictionary that mapped regular
 expressions to namespace providing functions (with sensible defaults).
 Something like
\layout Standard

completed = {
\newline 
'^cd
\backslash 
s+(.*)' : complete_files_and_dirs,
\newline 
'^run
\backslash 
s+(.*)' : complete_files_and_dirs,
\newline 
'^run
\backslash 
s+(-.*)' : complete_run_options,
\newline 
}
\layout Standard

I don't know if this is feasible, but I really like programmed completions,
 which I use extensively in tcsh.
 My feeling is that something like this is eminently doable in ipython.
\layout Standard

/JDH
\layout Standard

For something like this to work cleanly, the magic command system needs
 also a clean options framework, so all valid options for a given magic
 can be extracted programatically.
\layout Section

Debugger
\layout Standard

Current system uses a minimally tweaked pdb.
 Fine-tune it a bit, to provide at least:
\layout Itemize

Tab-completion in each stack frame.
 See email to Chris Hart for details.
\layout Itemize

Object information via ? at least.
 Break up magic_oinfo a bit so that pdb can call it without loading all
 of IPython.
 If possible, also have the other magics for object study: doc, source,
 pdef and pfile.
\layout Itemize

Shell access via !
\layout Itemize

Syntax highlighting in listings.
 Use py2html code, implement color schemes.
\layout Section

A Python-based system shell - pysh?
\layout Standard

Note: as of IPython 0.6.1, most of this functionality has actually been implemente
d.
\layout Standard

This section is meant as a working draft for discussions on the possibility
 of having a python-based system shell.
 It is the result of my own thinking about these issues as much of discussions
 on the ipython lists.
 I apologize in advance for not giving individual credit to the various
 contributions, but right now I don't have the time to track down each message
 from the archives.
 So please consider this as the result of a collective effort by the ipython
 user community.
\layout Standard

While IPyhton is (and will remain) a python shell first, it does offer a
 fair amount of system access functionality:
\layout Standard

- ! and !! for direct system access,
\layout Standard

- magic commands which wrap various system commands,
\layout Standard

- @sc and @sx, for shell output capture into python variables,
\layout Standard

- @alias, for aliasing system commands.
\layout Standard

This has prompted many users, over time, to ask for a way of extending ipython
 to the point where it could be used as a full-time replacement over typical
 user shells like bash, csh or tcsh.
 While my interest in ipython is such that I'll concentrate my personal
 efforts on other fronts (debugging, architecture, improvements for scientific
 use, gui access), I will be happy to do anything which could make such
 a development possible.
 It would be the responsibility of someone else to maintain the code, but
 I would do all necessary architectural changes to ipython for such an extension
 to be feasible.
\layout Standard

I'll try to outline here what I see as the key issues which need to be taken
 into account.
 This document should be considered an evolving draft.
 Feel free to submit comments/improvements, even in the form of patches.
\layout Standard

In what follows, I'll represent the hypothetical python-based shell ('pysh'
 for now) prompt with '>>'.
\layout Subsection

Basic design principles
\layout Standard

I think the basic design guideline should be the following: a hypothetical
 python system shell should behave, as much as possible, like a normal shell
 that users are familiar with (bash, tcsh, etc).
 This means:
\layout Standard

1.
 System commands can be issued directly at the prompt with no special syntax:
\layout Standard

>> ls
\layout Standard

>> xemacs
\layout Standard

should just work like a user expects.
\layout Standard

2.
 The facilities of the python language should always be available, like
 they are in ipython:
\layout Standard

>> 3+4 
\newline 
7
\layout Standard

3.
 It should be possible to easily capture shell output into a variable.
 bash and friends use backquotes, I think using a command (@sc) like ipython
 currently does is an acceptable compromise.
\layout Standard

4.
 It should also be possible to expand python variables/commands in the middle
 of system commands.
 I thihk this will make it necessary to use $var for name expansions:
\layout Standard

>> var='hello' # var is a Python variable 
\newline 
>> print var hello # This is the result of a Python print command 
\newline 
>> echo $var hello # This calls the echo command, expanding 'var'.
\layout Standard

5.
 The above capabilities should remain possible for multi-line commands.
 One of the most annoying things I find about tcsh, is that I never quite
 remember the syntactic details of looping.
 I often want to do something at the shell which involves a simple loop,
 but I can never remember how to do it in tcsh.
 This often means I just write a quick throwaway python script to do it
 (Perl is great for this kind of quick things, but I've forgotten most its
 syntax as well).
\layout Standard

It should be possible to write code like:
\layout Standard

>> for ext in ['.jpg','.gif']: 
\newline 
..
 ls file$ext
\layout Standard

And have it work as 'ls file.jpg;ls file.gif'.
\layout Subsection

Smaller details 
\layout Standard

If the above are considered as valid guiding principles for how such a python
 system shell should behave, then some smaller considerations and comments
 to keep in mind are listed below.
\layout Standard

- it's ok for shell builtins (in this case this includes the python language)
 to override system commands on the path.
 See tcsh's 'time' vs '/usr/bin/time'.
 This settles the 'print' issue and related.
\layout Standard

- pysh should take
\layout Standard

foo args
\layout Standard

as a command if (foo args is NOT valid python) and (foo is in $PATH).
\layout Standard

If the user types
\layout Standard

>> ./foo args
\layout Standard

it should be considered a system command always.
\layout Standard

- _, __ and ___ should automatically remember the previous 3 outputs captured
 from stdout.
 In parallel, there should be _e, __e and ___e for stderr.
 Whether capture is done as a single string or in list mode should be a
 user preference.
 If users have numbered prompts, ipython's full In/Out cache system should
 be available.
\layout Standard

But regardless of how variables are captured, the printout should be like
 that of a plain shell (without quotes or braces to indicate strings/lists).
 The everyday 'feel' of pysh should be more that of bash/tcsh than that
 of ipython.
\layout Standard

- filename completion first.
 Tab completion could work like in ipython, but with the order of priorities
 reversed: first files, then python names.
\layout Standard

- configuration via standard python files.
 Instead of 'setenv' you'd simply write into the os.environ[] dictionary.
 This assumes that IPython itself has been fixed to be configured via normal
 python files, instead of the current clunky ipythonrc format.
\layout Standard

- IPython can already configure the prompt in fairly generic ways.
 It should be able to generate almost any kind of prompt which bash/tcsh
 can (within reason).
\layout Standard

- Keep the Magics system.
 They provide a lightweight syntax for configuring and modifying the state
 of the user's session itself.
 Plus, they are an extensible system so why not give the users one more
 tool which is fairly flexible by nature? Finally, having the @magic optional
 syntax allows a user to always be able to access the shell's control system,
 regardless of name collisions with defined variables or system commands.
\layout Standard

But we need to move all magic functionality into a protected namespace,
 instead of the current messy name-mangling tricks (which don't scale well).
 
\layout Section

Future improvements
\layout Itemize

When from <mod> import * is used, first check the existing namespace and
 at least issue a warning on screen if names are overwritten.
\layout Itemize

Auto indent? Done, for users with readline support.
\layout Subsection

Better completion a la zsh
\layout Standard

This was suggested by Arnd:
\layout Standard

> >\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 More general, this might lead to something like
\layout Standard

> >\SpecialChar ~
\SpecialChar ~
\SpecialChar ~
 command specific completion ?
\layout Standard

>
\layout Standard

> I'm not sure what you mean here.
\layout Standard

\SpecialChar ~

\layout Standard

Sorry, that was not understandable, indeed ...
\layout Standard

I thought of something like
\layout Standard

\SpecialChar ~
- cd and then use TAB to go through the list of directories
\layout Standard

\SpecialChar ~
- ls and then TAB to consider all files and directories
\layout Standard

\SpecialChar ~
- cat and TAB: only files (no directories ...)
\layout Standard

\SpecialChar ~

\layout Standard

For zsh things like this are established by defining in .zshrc
\layout Standard

\SpecialChar ~

\layout Standard

compctl -g '*.dvi' xdvi
\layout Standard

compctl -g '*.dvi' dvips
\layout Standard

compctl -g '*.tex' latex
\layout Standard

compctl -g '*.tex' tex
\layout Standard

...
\layout Section

Outline of steps
\layout Standard

Here's a rough outline of the order in which to start implementing the various
 parts of the redesign.
 The first 'test of success' should be a clean pychecker run (not the mess
 we get right now).
\layout Itemize

Make Logger and Magic not be mixins but attributes of the main class.
 
\begin_deeper 
\layout Itemize

Magic should have a pointer back to the main instance (even if this creates
 a recursive structure) so it can control it with minimal message-passing
 machinery.
 
\layout Itemize

Logger can be a standalone object, simply with a nice, clean interface.
\layout Itemize

Logger currently handles part of the prompt caching, but other parts of
 that are in the prompts class itself.
 Clean up.
\end_deeper 
\layout Itemize

Change to python-based config system.
\layout Itemize

Move make_IPython() into the main shell class, as part of the constructor.
 Do this 
\emph on 
after 
\emph default 
the config system has been changed, debugging will be a lot easier then.
\layout Itemize

Merge the embeddable class and the normal one into one.
 After all, the standard ipython script 
\emph on 
is
\emph default 
 a python program with IPython embedded in it.
 There's no need for two separate classes (
\emph on 
maybe
\emph default 
 keep the old one around for the sake of backwards compatibility).
\layout Section

Ville Vainio's suggestions
\layout Standard

Some notes sent in by Ville Vainio 
\family typewriter 
<vivainio@kolumbus.fi>
\family default 
 on Tue, 29 Jun 2004.
 Keep here for reference, some of it replicates things already said above.
\layout Standard

Current ipython seems to "special case" lots of stuff - aliases, magics
 etc.
 It would seem to yield itself to a simpler and more extensible architecture,
 consisting of multple dictionaries, where just the order of search is determine
d by profile/prefix.
 All the functionality would just be "pushed" to ipython core, i.e.
 the objects that represent the functionality are instantiated on "plugins"
 and they are registered with ipython core.
 i.e.
\layout Standard

def magic_f(options, args): pass
\layout Standard

m = MyMagic(magic_f) m.arghandler = stockhandlers.OptParseArgHandler m.options
 = ....
 # optparse options, for easy passing to magic_f and help display
\layout Standard

# note that arghandler takes a peek at the instance, sees options, and proceeds
 # accordingly.
 Various arg handlers can ask for arbitrary options.
 # some handler might optionally glob the filenames, search data folders
 for filenames etc.
\layout Standard

ipythonregistry.register(category = "magic", name = "mymagic", obj = m)
\layout Standard

I bet most of the current functionality could easily be added to such a
 registry by just instantiating e.g.
 "Magic" class and registering all the functions with some sensible default
 args.
 Supporting legacy stuff in general would be easy - just implement new handlers
 (arg and otherwise) for new stuff, and have the old handlers around forever
 / as long as is deemed appropriate.
 The 'python' namespace (locals() + globals()) should be special, of course.
\layout Standard

It should be easy to have arbitrary number of "categories" (like 'magic',
 'shellcommand','projectspecific_myproject', 'projectspecific_otherproject').
 It would only influence the order in which the completions are suggested,
 and in case of name collision which one is selected.
 Also, I think all completions should be shown, even the ones in "later"
 categories in the case of a match in an "earlier" category.
\layout Standard

The "functionality object" might also have a callable object 'expandarg',
 and ipython would run it (with the arg index) when tab completion is attempted
 after typing the function name.
 It would return the possible completions for that particular command...
 or None to "revert to default file completions".
 Such functionality could be useful in making ipython an "operating console"
 of a sort.
 I'm talking about:
\layout Standard

>> lscat reactor # list commands in category - reactor is "project specific"
 category
\layout Standard

r_operate
\layout Standard

>> r_operate <tab> start shutdown notify_meltdown evacuate
\layout Standard

>> r_operate shutdown <tab>
\layout Standard

1 2 5 6 # note that 3 and 4 are already shut down
\layout Standard

>> r_operate shutdown 2
\layout Standard

Shutting down..
 ok.
\layout Standard

>> r_operate start <tab>
\layout Standard

2 3 4 # 2 was shut down, can be started now
\layout Standard

>> r_operate start 2
\layout Standard

Starting....
 ok.
\layout Standard

I'm talking about having a super-configurable man-machine language here!
 Like cmd.Cmd on steroids, as a free addition to ipython!
\the_end