canvas.bbox returns None on 'hidden' items while coords doesn't

[yutanicorp]

BPO	43462
Nosy	@terryjreedy, @serhiy-storchaka, @E-Paine, @yutanicorp

^{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 2021-03-13.09:05:49.375>
created_at = <Date 2021-03-10.13:51:23.888>
labels = ['3.7', 'invalid', 'type-bug', 'expert-tkinter']
title = "canvas.bbox returns None on 'hidden' items while coords doesn't"
updated_at = <Date 2021-03-13.09:05:49.375>
user = 'https://github.com/yutanicorp'

bugs.python.org fields:

activity = <Date 2021-03-13.09:05:49.375>
actor = 'Vincent'
assignee = 'none'
closed = True
closed_date = <Date 2021-03-13.09:05:49.375>
closer = 'Vincent'
components = ['Tkinter']
creation = <Date 2021-03-10.13:51:23.888>
creator = 'Vincent'
dependencies = []
files = []
hgrepos = []
issue_num = 43462
keywords = []
message_count = 8.0
messages = ['388432', '388439', '388450', '388502', '388504', '388505', '388581', '388597']
nosy_count = 4.0
nosy_names = ['terry.reedy', 'serhiy.storchaka', 'epaine', 'Vincent']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43462'
versions = ['Python 3.7']

[yutanicorp]

canvas.bbox() should return a tuple containing values whether an item is hidden or not. canvax.coords() does return a tuple when an item is hidden.

Steps to reproduce:

  from tkinter import * 
  root = Tk()
  canvas = Canvas(root)
  id1 = canvas.create_line(10,5,20,5, tags='tunnel')
  id2 = canvas.create_line(10,8,20,8, tags='tunnel')
  canvas.bbox('tunnel')   # return a tupple
  canvas.itemconfig('tunnel', state='hidden')
  canvas.bbox('tunnel')   # return nothing not even None

I need bbox to return a tuple containing values. The consequences is that the code must make the items temporarily visible before it can invoke the bbox function. This turning on and off creates flashing items in my program.

Thanks in advance!

[serhiy-storchaka]

What do you mean by "return nothing not even None"? Does it hang?

[yutanicorp]

No, not hang. It returns a NoneType.

See this example:

>>> x = canvas.bbox('tunnel')
>>> type(x)
<class 'NoneType'>
>>>

[E-Paine]

This can be easily reproduced in Wish (8.6.11):

% pack [canvas .c]
% .c create rectangle 10 10 90 90
1
% .c bbox 1
9 9 91 91
% .c create rectangle 20 20 80 80 -state hidden
2
% .c bbox 2
%

I doubt this is a bug because the docs (https://www.tcl.tk/man/tcl8.6/TkCmd/canvas.htm#M36) say:

if the matching items have empty bounding boxes (i.e. they have nothing to display) then an empty string is returned

[yutanicorp]

Thank you for your comments. Yes, I would doubt that, too. You would expect to get a bounding box regardless what state the canvas item are in. The only way to fix this (and I'm open to suggestions), is to create a (custom) function that calculate every object belonging to a specific tag and add/subtract the coordinates - this is cumbersome.

[yutanicorp]

... calculate the coordinates using the canvas.coords function

[terryjreedy]

(You don't use coords('tunnel') above because it only reports on the 'first' tagged object.)

tkinter widget methods are generally thin wrappers around tk functions that translate between python objects and tk strings.

I believe that this should be closed as '3rd party' or 'not a bug'.

[yutanicorp]

HI Terry, yes, that's completely true. But what I meant is I have to invoke coords on every item belonging to a tag and then perform some calculations to get the boundary box of all the items belonging to the item.

Let's close this issue and I will knock on the door of the developers of Tk.