Named widget has NoneType after single line creation

[rcrosser]

BPO	44971
Nosy	@stevendaprano
Files	test_pack.py: python code. Works with the top 3 buttons, crashes with the lower 3 buttons.

^{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 2021-08-21.16:00:34.153>
created_at = <Date 2021-08-21.14:55:34.791>
labels = ['invalid', 'type-bug', 'expert-tkinter', '3.9']
title = 'Named widget has NoneType after single line creation'
updated_at = <Date 2021-08-21.16:00:34.151>
user = 'https://bugs.python.org/rcrosser'

bugs.python.org fields:

activity = <Date 2021-08-21.16:00:34.151>
actor = 'steven.daprano'
assignee = 'none'
closed = True
closed_date = <Date 2021-08-21.16:00:34.153>
closer = 'steven.daprano'
components = ['Tkinter']
creation = <Date 2021-08-21.14:55:34.791>
creator = 'rcrosser'
dependencies = []
files = ['50228']
hgrepos = []
issue_num = 44971
keywords = []
message_count = 2.0
messages = ['400032', '400034']
nosy_count = 2.0
nosy_names = ['steven.daprano', 'rcrosser']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44971'
versions = ['Python 3.9']

[rcrosser]

Declaring a widget in the following form:
...
label2 = ttk.Label(root, text='Show2 Label').pack()
...
leaves the widget with a NoneType, and unable to be assigned to (for instance to assign new text). If giving a widget a name, I expect to use it later in the program.
This declaration works correctly:
...
label2 = ttk.Label(root, text='Show2 Label')
label2.pack()
...
Simple tkinter program attached. Only tested with 3.9.6 on Win 10.

[stevendaprano]

I'm sorry if you don't like the design of the pack() method, but all the examples in the documentation show how it behaves. It is behaving as documented and designed.

https://docs.python.org/3/library/tkinter.html

The bug here is in your own code. You already know the correct way to write this, as you already stated:

    label2 = ttk.Label(root, text='Show2 Label')
    label2.pack()

Writing it as ttk.Label(root, text='Show2 Label').pack() returns None, as designed, which then consequently fails when you try to operate on None.

You say:

"If giving a widget a name, I expect to use it later in the program."

But you don't give the widget a name. What you are doing is the equivalent of this:

    temp = ttk.Label(root, text='Show2 Label')  # hidden temp object
    label = temp.pack()  # Returns None
    del temp  # hidden temp object is garbage collected

except that temp is never directly accessible by you.

Or if you prefer another analogy:

    number = (1 + 2) - 3

and then get surprised that number is zero rather than 3 because "I gave (1+2) a name". No, you gave a name to the *whole expression*, which evaluates to 0, not 3. And in the Label case, the *whole expression* evaluates to None.

Also, the code doesn't crash. It raises an exception, which is the expected behaviour for trying to access non-existent attributes.