[Python-bugs-list] [ python-Bugs-411996 ] no "_" variable with displayhook

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Bugs item #411996, was updated on 2001-03-28 12:09
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Category: None
>Group: Not a Bug
Status: Open
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
>Summary: no "_" variable with displayhook

Initial Comment:
after using the new displayhook function, the "_" 
variable is no longer functional.

>>> # Create a recursive data structure
... L = [1,2,3]
>>> L.append(L)
>>> L # Show Python's default output
[1, 2, 3, [...]]
>>> # Use pprint.pprint() as the display function
... import sys, pprint
>>> sys.displayhook = pprint.pprint
>>> L
[1, 2, 3,  <Recursion on list with id=135143996>]
>>> a = 1./4
>>> _
[1, 2, 3, <Recursion on list with id=135525660>] 





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>Comment By: Tim Peters (tim_one)
Date: 2001-03-28 20:00

Message:
Logged In: YES 
user_id=31435

Sorry, but setting "_" is done by the system-default 
display hook.  If you replace the default display hook, you 
lose it.  If you still want it, you have to implement it in 
*your* display hook (by assigning to __builtin__._ when you 
want its value to change).

Note that the example you gave is a bad one, because an 
assignment statement doesn't trigger the display hook 
anyway.  That is, "a = 1./4" would have had no effect on _ 
even if you hadn't replaced the display hook.

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