On 3/9/2023 3:29 AM, aapost wrote:
The 'what I am trying to do' is ask a question regarding opinions and
practices on issuing a sequence of actions within a lambda via a tuple
(since the common practice approaches against it - mainly with tkinter -
feel more convoluted), and in doing so leaving it open ended to get a
feel on what opinions are, and to see if any opinions influence mine.
I finally realized why I am uncomfortable with doing this kind of thing.
It's because, IMHO, lambda expressions should not have side effects
and should not require much mental effort to grasp what they do. Yes,
you can do so. You can even print from a lambda (and it might be useful
for debugging):
lambda x: print(f'The lambda received {x}') or x*x
The Python Reference on readthedocs.io also has a tk example that
specifically wants the side effect (see
https://python-reference.readthedocs.io/en/latest/docs/operators/lambda.html):
>>> # this is a code snippet from a Tkinter gui app
>>> # in this case lambda is quite convenient
>>> self.btn_cancel = Button(self.progress_container, text='Cancel',
>>> command=lambda: subprocess.call('taskkill /f /im uberzip.exe',
>>> shell=True))
Maybe so, but I think it's better not to have side effects hidden away
in expressions that are hard to read and understand. And being
anonymous, there is no function name to remind you what the action is
suppose to do. Much better (still IMHO, of course):
def kill_uberzip():
"""Kill an external running program named uberzip.exe."""
subprocess.call('taskkill /f /im uberzip.exe', shell=True))
self.btn_cancel = Button(self.progress_container, text='Cancel',
command = kill_uberzip())
This way, it's easy to understand what btn_cancel() will do each time
you scan that line of code. Using the lambda makes you reparse the line
and spend mental effort each time you scan it. And this way, you know
directly that the button is going to cause a side effect outside your
program, which you have to infer (an indirect mental operation) when you
scan the lambda.
For this particular example, it might turn out that there could be more
than one instance of uberzip.exe running at the same time. Which one
should be killed, and how do you kill the right one? With the function,
you can get those details under control, but I hate to think what might
happen to the lambda expression.
Yes, of course, there can be times when the lambda expression is
somewhat easy to understand and the side effects are harmless. In that
case, it may be easy enough to grasp quickly that the anonymous function
would not benefit from having a name. So OK, it's not a hard-and-fast
rule.
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