[issue21161] list comprehensions don't see local variables in pdb in python3

[Andreas Kloeckner]

Change by Andreas Kloeckner :


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[issue21161] list comprehensions don't see local variables in pdb in python3

[daniel hahler]

Change by daniel hahler :


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pull_request: https://github.com/python/cpython/pull/15194

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[issue21161] list comprehensions don't see local variables in pdb in python3

[daniel hahler]

daniel hahler  added the comment:

Georg, please consider re-opening.
This patch here appears to fix this after all.

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versions: +Python 3.6, Python 3.7, Python 3.8, Python 3.9

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[issue21161] list comprehensions don't see local variables in pdb in python3

[Florent Xicluna]

Changes by Florent Xicluna florent.xicl...@gmail.com:


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[issue21161] list comprehensions don't see local variables in pdb in python3

[Xavier de Gaye]

Xavier de Gaye added the comment:

The patch fails to invoke exec() with the locals argument set to the current 
frame locals.
The attached patch fixes this, and test_pdb runs now fine with it.

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Added file: http://bugs.python.org/file35305/default.patch

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[issue21161] list comprehensions don't see local variables in pdb in python3

[Xavier de Gaye]

Xavier de Gaye added the comment:

Interestingly, the interact command was added at changeset:

$ hg log -v --pager cat -r $(hg blame Lib/pdb.py | grep do_interact | awk -F : 
'{print $1}')
changeset:   66691:c2578a68879d
user:Georg Brandl ge...@python.org
date:Sat Dec 04 11:20:26 2010 +
files:   Doc/library/pdb.rst Lib/pdb.py Misc/NEWS
description:
Add the interact pdb command from pdb++.


And the included documentation, added at that time, states (emphasis added by 
me):
Start an interative interpreter (using the code module) whose global namespace 
contains all the ***(global and local)*** names found in the current scope.


I can provide a test case for the patch when this issue is re-opened, unless 
someone else is willing to do it.

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[issue21161] list comprehensions don't see local variables in pdb in python3

[Xavier de Gaye]

Xavier de Gaye added the comment:

The NameError exception occuring on a generator expression referencing a local 
variable when the generator is called within exec() is the object of multiple 
entries in the bug tracker, see issue 13557.

msg 149096 in this issue suggests using exec(code, locals()) to fix the 
problem. It seems that what does currently the do_interact() method, and what 
is proposed in the patch is the recommended practice to handle this problem.

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[issue21161] list comprehensions don't see local variables in pdb in python3

[Xavier de Gaye]

Xavier de Gaye added the comment:

FWIW this generator expression can be evaluated with the 'interact' command:

--Return--
 /test/comprehension.py(5)foo()-None
- pdb.set_trace()
(Pdb) interact
*interactive*
 all(x  limit for x in items)
True
 
(Pdb)

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[issue21161] list comprehensions don't see local variables in pdb in python3

[Xavier de Gaye]

Xavier de Gaye added the comment:

The runcode() method of InteractiveInterpreter in code.py uses the 
'self.locals' dictionary as the 'globals' parameter of the invoked exec() 
function. And the do_interact() method of Pdb instantiates 
InteractiveInterpreter with 'locals' as a merge of the current frame's locals 
and globals dictionary. This explains why the interact command of pdb evaluates 
sucessfully the generator expression: the generator function object is 
evaluated by the interpreter in a frame where 'locals' is NULL (see 
fast_function() in ceval.c) and 'globals' includes now the debugged frame 
locals dictionary.

So a fix for this problem is to have the default() method of pdb be implemented 
in the same manner as do_interact() and the runcode() method of 
InteractiveInterpreter. The attached patch does this.

--
keywords: +patch
Added file: http://bugs.python.org/file34791/genexp.patch

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[issue21161] list comprehensions don't see local variables in pdb in python3

[Jurko Gospodnetić]

Jurko Gospodnetić added the comment:

Thanks for looking into this Xavier.

Could someone reopen this issue so it can gets looked at again?

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[issue21161] list comprehensions don't see local variables in pdb in python3

[Jurko Gospodnetić]

Jurko Gospodnetić added the comment:

Just ran into this problem and it's so uncomfortable
researching dynamic structures at run-time using PDB
without this. :-(

As a workaround, you can use a trick similar to this one
to 'import' your locals into the list comprehension body:

[l['r'](x) for l in (locals(),) for x in l['some_local']]

assuming 'r'  'some_local' are two local variables in
your surrounding scope.

Ugly, but at least it can be made/forced to work if needed...

Best regards,
  Jurko Gospodnetić

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[issue21161] list comprehensions don't see local variables in pdb in python3

[Kay]

New submission from Kay:

Using generators in pdb are very handy but since Python3 they don't work 
properly. For example:

import pdb
def foo():
  items = [1, 2, 3]
  limit = 5
  pdb.set_trace()

foo()

in pdb prompt the following fails:

(pdf) all(x  limit for x in items)
*** NameError: global name 'items' is not defined

I can express that in a lambda expression (i.e. pass items as an argument) but 
this seems unnecessary and very inelegant.

--
components: Interpreter Core
messages: 215595
nosy: kay
priority: normal
severity: normal
status: open
title: list comprehensions don't see local variables in pdb in python3
versions: Python 3.1, Python 3.2, Python 3.3

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[issue21161] list comprehensions don't see local variables in pdb in python3

[Kay]

Changes by Kay straitsai...@gmail.com:


--
type:  - behavior

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[issue21161] list comprehensions don't see local variables in pdb in python3

[R. David Murray]

Changes by R. David Murray rdmur...@bitdance.com:


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[issue21161] list comprehensions don't see local variables in pdb in python3

[Kay]

Changes by Kay straitsai...@gmail.com:


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[issue21161] list comprehensions don't see local variables in pdb in python3

[Georg Brandl]

Georg Brandl added the comment:

Your failure appears to be not pasted from an interpreter session; the actual 
failure is:

(Pdb) all(x  limit for x in items)
*** NameError: global name 'limit' is not defined

(i.e. limit is not found, not items).  This actually does not work in 
Python 2 either.  What did work in Python 2 and doesn't work in 3, is using a 
list comprehension like

all([x  limit for x in items])

This is because list comprehensions are now implemented with their own function 
object like generator expressions have always been.  To make the code in pdb 
compile as if it was put in the debugged function will be as good as 
impossible, so I'm closing this as won't fix.

--
resolution:  - wont fix
status: open - closed

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