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PEP 572: Python assignment expressions has been accepted

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317 points est | 8 comments | 03 Jul 18 08:30 UTC | HN request time: 1.324s | source | bottom
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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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1. kibibu ◴[03 Jul 18 09:06 UTC] No.17448591[source]▶
High-level overview: it's an assignment operator that returns its value, similar to C's assignment operator.

The choice of := is to avoid accidentally using assignment where comparison is expected.

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2. arketyp ◴[03 Jul 18 09:38 UTC] No.17448770[source]▶
I feel the colon is unnecessary, especially considering how C deals with this. A plain '=' inside a conditional is already invalid syntax in Python.
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3. heavenlyblue ◴[03 Jul 18 09:42 UTC] No.17448792[source]▶
No, it's necessary.
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4. detaro ◴[03 Jul 18 09:45 UTC] No.17448811[source]▶
And it's a very well-known source of bugs in C, since it's to close to "==". I don't think new languages adopting that is a good idea.
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5. arketyp ◴[03 Jul 18 09:59 UTC] No.17448898{3}[source]▶
How so? Syntactically, or from a pragmatic point of view?
6. arketyp ◴[03 Jul 18 10:02 UTC] No.17448913{3}[source]▶
Sure. But if fidelity to C style was not a concern then I don't see why the '==' syntax was adopted in the first place.
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7. detaro ◴[03 Jul 18 13:55 UTC] No.17450177{4}[source]▶
== is an incredibly common syntax for equality and stand-alone not a problem. only if you introduce = to expressions too it becomes a risk. (well, you could theoretically accidentally write == for a normal assignment, but that kind of error is caught more easily)
8. bluecalm ◴[03 Jul 18 20:58 UTC] No.17453569[source]▶
Yeah but there is already solution for that in C: put parenthesis around assignment when using its value as bool. The compilers warn if you don't so making this error in C can only happen if you don't use warnings.