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PEP 572: Python assignment expressions has been accepted

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317 points est | 2 comments | 03 Jul 18 08:30 UTC | HN request time: 0.665s | source
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oooooof ◴[03 Jul 18 09:00 UTC] No.17448560[source]▶
What is it? The link points to a discussion more deep than I’m willing to read.
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est ◴[03 Jul 18 09:03 UTC] No.17448572[source]▶
It's a controversial PEP https://www.python.org/dev/peps/pep-0572/ which allows you to write Python like this:

    def foo():
        if n := randint(0, 3):
            return n ** 2
        return 1337


    [(x, y, x/y) for x in input_data if (y := f(x)) > 0]
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sluukkonen ◴[03 Jul 18 09:31 UTC] No.17448731[source]▶
Would've making regular assignment an expression broken too much existing code?
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1. sametmax ◴[03 Jul 18 10:45 UTC] No.17449059[source]▶
It's a voluntary design choice since the beginning of Python to avoid the very common mistake of doing:

    while continue = "yes":
instead of:

    while continue == "yes":
Those mistakes introduce bugs that are hard to spot because they don't cause an immediate error, linters can hardly help with them and even a senior can make them while being tired.
replies(1): >>17453480 #
2. bluecalm ◴[03 Jul 18 20:44 UTC] No.17453480[source]▶
I don't know about linters but GCC warns me about that every time I make that typo. They could just require parenthesis when assignment value is used as boolean.