[IPython-dev] Should IPython be a singleton?

[Robert Kern]

On 2009-08-26 18:17 PM, Brian Granger wrote:
>
>     When tracking down problems like this, one thing you have to be very
>     careful
>     about is not creating references via your instrumentation. It's
>     disturbingly
>     easy to do. :-)
>
>
> Yes, it is very tough to do right.
>
>     __builtins__.__IPYTHON__ and __builtins__.__IPYTHON__active are two
>     culprits,
>     and the remaining one is a cell object. I'm not sure where he is
>     coming from.
>
>
> In my version, I have gotten rid of __IPYTHON__ and IPYTHON_active is an
> int.
>
> What is a cell object?

It is created when there are closures.

http://docs.python.org/c-api/cell.html

> Could I see the foo.py script?

Oops! Sorry. I thought I catted it. Here it is with a few more things cleaned up.

[~]$ cat foo.py
import gc
import sys
import types

from IPython.core.shell import InteractiveShell

real_main = sys.modules['__main__']

s = InteractiveShell('foo')
print s

# Clean up.
del s.shell
del s
del __builtins__.__IPYTHON__active
del __builtins__.__IPYTHON__
if hasattr(sys, 'ipcompleter'):
     del sys.ipcompleter
sys.stdin = sys.__stdin__
sys.stdout = sys.__stdout__
sys.stderr = sys.__stderr__
sys.displayhook = sys.__displayhook__
sys.excepthook = sys.__excepthook__
sys.modules['__main__'] = real_main

for obj in gc.get_objects():
     if getattr(type(obj), '__name__', None) == 'InteractiveShell':
         print obj
         refs = gc.get_referrers(obj)
         print '%s references:' % len(refs)
         for ref in refs:
             print type(ref)
             if isinstance(ref, dict):
                 print 'A dict with keys: %r' % (ref.keys(),)
             elif isinstance(ref, list):
                 print 'A list of %s elements; probably gc.get_objects().' % 
len(ref)
             elif type(ref).__name__ == 'cell':
                 print 'A cell: %r' % ref
                 print ref.cell_contents
             else:
                 print ref
             print


-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco