tkFont may reuse font names

[effbot]

BPO	802310
Nosy	@asvetlov
Files	tkfont_bug.py nonamerepeat.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 = 'https://github.com/asvetlov'
closed_at = <Date 2012-04-03.06:51:05.975>
created_at = <Date 2003-09-08.07:52:56.000>
labels = ['type-bug', 'expert-tkinter']
title = 'tkFont may reuse font names'
updated_at = <Date 2012-04-03.06:51:05.973>
user = 'https://bugs.python.org/effbot'

bugs.python.org fields:

activity = <Date 2012-04-03.06:51:05.973>
actor = 'asvetlov'
assignee = 'asvetlov'
closed = True
closed_date = <Date 2012-04-03.06:51:05.975>
closer = 'asvetlov'
components = ['Tkinter']
creation = <Date 2003-09-08.07:52:56.000>
creator = 'effbot'
dependencies = []
files = ['1024', '14332']
hgrepos = []
issue_num = 802310
keywords = ['patch']
message_count = 7.0
messages = ['18102', '18103', '64948', '89581', '114268', '157394', '157395']
nosy_count = 6.0
nosy_names = ['effbot', 'lpd', 'gpolo', 'asvetlov', 'BreamoreBoy', 'python-dev']
pr_nums = []
priority = 'low'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue802310'
versions = ['Python 3.3']

[effbot]

(sent to me instead of to the bug manager; note that
the tkFont naming approach is also used for widgets and
callbacks /F)

The class tkFont has a problem name it chooses if no
name is
given. The choosen method 'name = "font" + str(id
(self))' isn't safe
because the name may exists longer than the Font
object and so another
Font object may be created with a different font but the
same
id() and so the same name. id() says

Return the identity of an object.  This is guaranteed 

to be unique
among simultaneously existing objects.
^^^^^^^^^^^^^^^^^^^^^^^

Note that this bug doesn't strike if you hold a reference
to the Font
object and so the GC can't reclaim the space.

To reproduce run the attached program. It produces
something like:

previously: ('Times', 15, 'bold')
now: ('Times', 18, 'bold')
iterations: 8
mapping: {'font136494612': ('Times', 
14, 'bold'), 'font136499772': ('Times', 
15, 'bold'), 'font136545468': ('Times', 
17, 'bold'), 'font136483156': ('Times', 
11, 'bold'), 'font136502700': ('Times', 
12, 'bold'), 'font136510460': ('Times', 
13, 'bold'), 'font136515228': ('Times', 
16, 'bold'), 'font136365348': ('Times', 10, 'bold')}
Traceback (most recent call last):
  File "tkfont_bug.py", line 20, in ?
    assert 0
AssertionError

Raimar

[lpd]

This bug has bitten me too, in a real program.

[gpolo]

This still happens, but around 2000 iterations here on newer Python
versions (trunk, 3alpha, 2.5.x, 2.4.x). Using Python 1.6 I've got it at
2 iterations (min), but.. is this going to be fixed or given the amount
of iterations needed nowadays this is no longer a problem ? If it should
be fixed, are there any suggestions on how to proceed ?

[gpolo]

Uhm, now I'm getting it at around 3 iterations with python-trunk. So,
can't we just use a simple generator for this ? Patch attached.

The same could be done for widget and callback naming.

[BreamoreBoy]

Patch is really simple and looks ok to me, can we get this committed please.

[python-dev]

New changeset a77e23135675 by Andrew Svetlov in branch 'default':
Issue bpo-802310: Generate always unique tkinter font names if not directly passed
http://hg.python.org/cpython/rev/a77e23135675

[asvetlov]

I've pushed fix inspired by Guilherme's suggestion.

Fix has been applied to 3.3 only because:

1. It changes font name generation schema
2. It's definitelly minor issue as exists starting from 2003.

Thanks.