[IPython-dev] ipipe news

Walter Dörwald walter at livinglogic.de
Fri Mar 3 03:34:38 EST 2006

Fernando Perez wrote:
> Walter Dörwald wrote:
>> [...]
>> But as you get '0 objects' this probably means that you don't have any 
>> Python source files in your current directory.
> No, that's not the case:
> In [4]: ls *.py
> argv.py*  cf.py   env.py*    exit2.py*     sciweave.py  vars.py
> avg.py*   die.py  error.py*  exit.py*      scopes.py*   xplot.py*
> bar.py    div.py  err.py     ramptest.py*  strings.py
> And in addition, I thought it was recursive, so I thought it would work 
> even if the parent directory had no .py files (as long as subdirs had 
> them).

It does.

>> What happens if you do a simple "iwalk"?
> That works fine.  But
> iwalk | ifilter("name.endswith('.py')")
> gives an empty browser, and
> iwalk | isort("size")
> produces a lovely traceback (here's just the end of it, let me know if 
> you want a full one in verbose mode, I'll attach it).
> [...] 
> /home/fperez/usr/lib/python2.3/site-packages/IPython/Extensions/ipipe.py 
> in key(item)
>     984         else:
>     985             def key(item):
> --> 986                 return eval(self.key, globals(), 
> _AttrNamespace(item))
>     987             items = sorted(
>     988                 xiter(self.input, mode),
> TypeError: eval() argument 3 must be dict, not _AttrNamespace

I see: ipipe uses a new feature of eval() that makes it possible to pass 
a custom (non-dict) namespace. This makes it possible to directly 
reference the attributes of the object. For 2.3 compatibility I see 
several options:

1) Simply don't allow expression strings. This would only allow 
callables and
    iwalk | ifilter("name.endswith('.py')") | isort("size")
would turn into
    iwalk | ifilter(lambda _:_.name.endswith('.py')) | isort(lambda _:_size)
IMHO not so nice.

2) Pass a simple dictionary to eval() that just contains the object 
itself. The call would then look like this
    iwalk | ifilter("_.name.endswith('.py')") | isort("_.size")

3) Pass a dictionary that contains all the attributes from the list. 
This has the disadvantage that (for iwalk etc.) there will be many 
os.stat() calls, even if the result is never used (and you can't 
reference attributes that are not in the field list).

BTW, the reason why you got an empty browser was, because ifilter 
ignores all objects where evaluating the expression raises and 
Exception. And then the expression for isort never fails, because 
there's nothing left to sort.

Anyway, IMHO we should implement 2) and document the possibility to 
directly reference attributes as a "2.4 goodie".


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