[IPython-dev] Re: [IPython-user] pysh is in CVS

Fernando Perez Fernando.Perez at colorado.edu
Mon Jun 28 11:14:04 EDT 2004

Daniel 'Dang' Griffith wrote:
>     Wow!  I had a minor problems because there some executables
> in my path with the same names as some Windows built-ins (e.g.,
> dir.exe, mkdir.exe, rmdir.exe).  After running rehashx, IPython was
> running them, rather than the built-in.  I was unaware of their 
> presence until this time; I deleted them, and life is good again.

Yes, this is a bit of an annoyance.  It is in principle possible to have 
multiple internal namespaces for commands, I just didn't want to deal with 
such hassles for now.  A true shell (bash, tcsh, etc) keeps at least 3 
namespaces: $PATH commands, user aliases and shell builtins.  For ipython's 
shell functionality, I've lumped all these into one, since I already have to 
worry about managing the magic and python language namespaces as well.  But it 
might be a good idea to at least have two: one for commands and one for user 

It's not that hard, just a bit time-consuming because the two dicts have to be 
managed carefully so it remains transparent to the user and doesn't slow 
things down noticeably.  Keep in mind that ipython has to remain responsive 
enough that you don't really notice any delay after pressing <Return>.  This 
means that whatever fancy magic it does, has to be finished in about 0.1s, 
which is roughly the human threshold for noticing 'slugishness'.  So I try 
very hard to keep the mainloop very tight so as to respect this constraint on 
reasonable hardware (my laptop is a 1.1GHz P-III, so I think it's a good 
middle-of-the-road benchmark these days).  If you actually look at the code, 
you'll see that I'm using a fairly stretchy definiton of 'tight' here, but 
that's a topic for another day.  Let's just say that I try my best :)

>     Great update!  I'll keep you posted if I see any strangenesses.
> It's really cool to be able to run 'jar', to access zip files, without 
> needing two windows open (an IPython and a command prompt).

Glad you like it!

> What do you mean about builtin piping?  I ask, because "ls /s | more" 
> works just fine.  And if I re-aliasing ls to ls.exe, "ls -R | less" works 
> just fine as well.

Yes, this works because the whole line is passed to the shell, which is the 
one handling the pipes.  What I meant was to write a bunch of _python_ 
utilities which simulate piping by overriding the '|' operator so you can 
simulate pipes in true python code.  There's an ASPN recipe on that if you 
feel like googling a bit.  I won't go that far, but as you correctly point 
out, 'regular' piping works just fine, courtesy of the underlying system shell.

Thanks for your report, and keep me posted on any issues you may encounter.



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