tkinter goes into an infinite loop (pydoc.gui)

[HWJ]

BPO	3835
Nosy	@loewis, @asvetlov
Files	issue_3835.diff issue_3835_2.diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2012-03-14.16:50:16.795>
created_at = <Date 2008-09-11.13:20:28.753>
labels = ['extension-modules', 'expert-tkinter', 'type-crash']
title = 'tkinter goes into an infinite loop (pydoc.gui)'
updated_at = <Date 2012-03-14.16:50:16.793>
user = 'https://bugs.python.org/HWJ'

bugs.python.org fields:

activity = <Date 2012-03-14.16:50:16.793>
actor = 'asvetlov'
assignee = 'none'
closed = True
closed_date = <Date 2012-03-14.16:50:16.795>
closer = 'asvetlov'
components = ['Extension Modules', 'Tkinter']
creation = <Date 2008-09-11.13:20:28.753>
creator = 'HWJ'
dependencies = []
files = ['11510', '24825']
hgrepos = []
issue_num = 3835
keywords = ['patch']
message_count = 15.0
messages = ['73021', '73237', '73259', '73265', '73302', '73303', '73304', '73324', '73332', '155640', '155664', '155665', '155763', '155764', '155765']
nosy_count = 5.0
nosy_names = ['loewis', 'gpolo', 'HWJ', 'asvetlov', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = None
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue3835'
versions = ['Python 3.3']

[HWJ]

With version 3.0 (SVN 66386)

import pydoc
pydoc.gui()

gives

>>> Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/local/lib/python3.0/threading.py", line 507, in 
_bootstrap_inner
    self.run()
  File "/usr/local/lib/python3.0/threading.py", line 462, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.0/pydoc.py", line 1989, in serve
    DocServer(port, callback).serve_until_quit()
  File "/usr/local/lib/python3.0/pydoc.py", line 1971, in __init__
    self.base.__init__(self, self.address, self.handler)
  File "/usr/local/lib/python3.0/socketserver.py", line 401, in __init__
    self.server_activate()
  File "/usr/local/lib/python3.0/pydoc.py", line 1982, in 
server_activate
    if self.callback: self.callback(self)
  File "/usr/local/lib/python3.0/pydoc.py", line 2072, in ready
    text='Python documentation server at\n' + server.url)
  File "/usr/local/lib/python3.0/tkinter/__init__.py", line 1199, in 
configure
    return self._configure('configure', cnf, kw)
  File "/usr/local/lib/python3.0/tkinter/__init__.py", line 1190, in 
_configure
    self.tk.call(_flatten((self._w, cmd)) + self._options(cnf))
_tkinter.TclError: out of stack space (infinite loop?)

[gpolo]

What tcl/tk version are you using ?

Also, can you put a "print(_flatten((self._w, cmd)) +
self._options(cnf))" before the line 1190 in
/usr/local/lib/python3.0/tkinter/init.py and tell what it shows when
you call pydoc.gui ?

[HWJ]

I'm using Tcl/Tk 8.5.4 here

        print(":::")
        print(_flatten((self._w, cmd)) + self._options(cnf))

produces:
:::
('.3073836300', 'configure', '-yscrollcommand', '3077632332set')
:::
('.3073835564.3073835660', 'configure', '-text', 'Python documentation 
server at\nhttp://localhost:7464/')
>>> Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/local/lib/python3.0/threading.py", line 507, in 
_bootstrap_inner
    self.run()
  File "/usr/local/lib/python3.0/threading.py", line 462, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.0/pydoc.py", line 1989, in serve
    DocServer(port, callback).serve_until_quit()
  File "/usr/local/lib/python3.0/pydoc.py", line 1971, in __init__
    self.base.__init__(self, self.address, self.handler)
  File "/usr/local/lib/python3.0/socketserver.py", line 401, in __init__
    self.server_activate()
  File "/usr/local/lib/python3.0/pydoc.py", line 1982, in 
server_activate
    if self.callback: self.callback(self)
  File "/usr/local/lib/python3.0/pydoc.py", line 2072, in ready
    text='Python documentation server at\n' + server.url)
  File "/usr/local/lib/python3.0/tkinter/__init__.py", line 1201, in 
configure
    return self._configure('configure', cnf, kw)
  File "/usr/local/lib/python3.0/tkinter/__init__.py", line 1192, in 
_configure
    self.tk.call(_flatten((self._w, cmd)) + self._options(cnf))
_tkinter.TclError: out of stack space (infinite loop?)

[gpolo]

Uhm, is it caused only by the combination of tk 8.5.4 and py3k, or does
the same happen with tk 8.5.4 and python-trunk ? What about tk 8.5.3 (or
some other of tk 8.5 series) or even tk 8.4.16 and {python-trunk, py3k} ?

It would be good if you could test some other combination, specially
because I can't reproduce it here with other versions (but I'm compiling
8.5.4 here now).

[gpolo]

Just reproduced the issue under python-trunk with tcl/tk 8.5.4 and 8.5.3

[gpolo]

But it happens only if you don't build tcl/tk with --enable-threads =)

[gpolo]

If you remove the widget.config calls in GUI.ready you will notice the
problem "goes away", but note that this method is called from another
thread while you have a non-thread-safe tcl/tk lib (I'm assuming you
didn't compile it with --enable-threads). So.. using multiple threads in
Python while Tcl is compiled without --enable-threads isn't supported at
all.

To reproduce the problem try this (change Tkinter to tkinter if py3k):

import threading
import Tkinter

lbl = Tkinter.Label(text="hi")
threading.Thread(target=lambda: lbl.configure(text="hi there")).start()
lbl.mainloop()

If your tcl/tk libs weren't compiled with --enable-threads this should
get you an "TclError: out of stack space (infinite loop?)". A
documentation note may be added somewhere, but nothing much else is
going to happen (that is what I believe at least).

[HWJ]

Many thanks, that solved the problem.

Since the cause of the problem wasn't easy to find out
(for me, at least)

would be possible to check at import time if Tcl/Tk has been
configured with threads enabled?

Helmut.

[gpolo]

The patch attached checks for that when an interpreter is created, not
really at import time but should be enough.

But my real concern is that tkinter thinks it will work properly when
Python is using threads and Tcl wasn't compiled with --enable-threads.
Maybe that was true some time ago or maybe in other platforms, but isn't
the case anymore.

[asvetlov]

Push updated patch for tip (3.3) head

[python-dev]

New changeset d731dcda2611 by Martin v. Löwis in branch 'default':
Issue bpo-3835: Refuse to use unthreaded Tcl in threaded Python.
http://hg.python.org/cpython/rev/d731dcda2611

[loewis]

Thanks for the patch!