Mailing List Archive

On Tue, Jan 04 2022 at 11:34:20 PM, NArshad <narshad.380@gmail.com> wrote:
> How to correct what is written below:
>
> Exception in Tkinter callback
> Traceback (most recent call last):
> File "C:\Users\Dani Brothers\Anaconda3\lib\tkinter\__init__.py", line 1705, in __call__
> return self.func(*args)
> File "D:/Python/Book Bank/New folder/PyCharm/Final/Excel.py", line 57, in SaveBook
> e_pissue.get(),
> AttributeError: 'NoneType' object has no attribute 'get'
>
> Process finished with exit code 0

The error means that e_pissue is None, so your code cannot call the get
method on it. You need to fix the code so that e_pissue is not None and
is instead referring to an object that has a suitable get method.

Without looking at the rest of your code, it is not possible to get any
more specific. Looking at the path of the file, it looks like you may
be following some programming exercises from a book. If so, perhaps you
need to look up the section about understanding exception tracebacks.

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regards,
kushal
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On 1/6/22 11:02, Kushal Kumaran wrote:
> On Tue, Jan 04 2022 at 11:34:20 PM, NArshad <narshad.380@gmail.com> wrote:
>> How to correct what is written below:
>>
>> Exception in Tkinter callback
>> Traceback (most recent call last):
>> File "C:\Users\Dani Brothers\Anaconda3\lib\tkinter\__init__.py", line 1705, in __call__
>> return self.func(*args)
>> File "D:/Python/Book Bank/New folder/PyCharm/Final/Excel.py", line 57, in SaveBook
>> e_pissue.get(),
>> AttributeError: 'NoneType' object has no attribute 'get'
>>
>> Process finished with exit code 0
>
> The error means that e_pissue is None, so your code cannot call the get
> method on it. You need to fix the code so that e_pissue is not None and
> is instead referring to an object that has a suitable get method.


And at a more meta level: many functions in the Python world return
None as an indication that the operation did not succeed. It's useful
because in many circumstances None is an "out of band" value - one that
could not happen naturally - and thus returning it provides an easy way
for the caller to check for success or failure.

However... if that is the case, you have to actually do that check. If
you just proceed as if a vaild value had come back, you're defeating the
purpose - and are sure to fall into a hole like the one you've encountered.
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On 2022-01-06 at 14:21:48 -0700,
Mats Wichmann <mats@wichmann.us> wrote:

> And at a more meta level: many functions in the Python world return
> None as an indication that the operation did not succeed. It's useful
> because in many circumstances None is an "out of band" value - one
> that could not happen naturally - and thus returning it provides an
> easy way for the caller to check for success or failure.

Errors should never pass silently.

Unless explicitly silenced.

https://www.infoq.com/presentations/Null-References-The-Billion-Dollar-Mistake-Tony-Hoare/

Exceptions aren't perfect, but when something fails, I'd much rather
have an exception raised and thrown at me than to get back None. An
exception is immediate,? but None often ends up causing trouble far
away? from where the actual failure occurred.

? in space and in time
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On Fri, Jan 7, 2022 at 8:47 AM <2QdxY4RzWzUUiLuE@potatochowder.com> wrote:
>
> On 2022-01-06 at 14:21:48 -0700,
> Mats Wichmann <mats@wichmann.us> wrote:
>
> > And at a more meta level: many functions in the Python world return
> > None as an indication that the operation did not succeed. It's useful
> > because in many circumstances None is an "out of band" value - one
> > that could not happen naturally - and thus returning it provides an
> > easy way for the caller to check for success or failure.
>
> Errors should never pass silently.
>
> Unless explicitly silenced.
>
> https://www.infoq.com/presentations/Null-References-The-Billion-Dollar-Mistake-Tony-Hoare/
>

Python is not C, and returning None is not the same as returning a
null pointer. Also, I dispute that null pointers are the
"billion-dollar mistake" described there, but of course, everyone
loves to talk about figures like that.

Returning None is most definitely not a flaw.

ChrisA
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