The challenge with anything like
result = default if bar is None else bar
or
result = bar if bar else default
or even
result = bar is None ? default : bar
is that sure default is only evaluated once - but in all cases 'bar' is
evaluated twice, and if bar is a function call then no parser is clever
enough to diagnose all possible side effects of calling bar() twice, or
even detect that bar can be cached, so it will always be called twice.
In Python then a better way might be
result = temp := bar() if temp else default
This way only bar() and default are evaluated and invoked once.
------ Original Message ------
From: "Rob Cliffe via Python-ideas" <python-ideas@python.org>
To: "Dom Grigonis" <dom.grigo...@gmail.com>; "Jothir Adithyan"
<adithyanjot...@gmail.com>
Cc: python-ideas@python.org
Sent: Monday, 17 Jul, 23 At 16:09
Subject: [Python-ideas] Re: Proposal for get_or function in Python
dictionaries
On 15/07/2023 21:08, Dom Grigonis wrote:
Just to add. I haven’t thought about evaluation.
Thus, to prevent evaluation of unnecessary code, introduction of
C-style expression is needed anyways:
1. result = bar is None ? default : bar
The below would have to evaluate all arguments, thus not
achieving benefits of PEP505.
2. result = ifelse(bar is None, default, bar)
So I would vote for something similar to:
result = bar is None ? default : bar
Where default and bar is only evaluated if needed. Although
not to the extent as initially intended, it would offer
satisfiable solutions to several proposals.
Well, default is only evaluated if needed; bar is always
evaluated.
What is wrong with the Python equivalent
result = default if bar is None else bar
or if you prefer
result = bar if bar is not None else default
Perhaps you didn't know about this construction?
It does exactly the same as the C version and is more readable.
Or am I missing something?
Best wishes
Rob Cliffe
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