What's Coming in Python 3.8

Re:What's Coming in Python 3.8 by Sohcahtoa82 on Wednesday July 17, 2019 @06:35PM (#20464720)

I see this criticism every time the walrus operator is brought up.

You do know that this:

    x := 1

Is going to be a syntax error, right? The walrus operator is not permitted in the case of a simple assignment statement. It's only in an expression.

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Re:What's Coming in Python 3.8 by Scarblac on Thursday July 18, 2019 @03:53AM (#20467711)

But it used to be that any expression on its own was a valid statement. Is that going to change?

When is an expression allowed to have := in it, is

  (x := 1)

on its own allowed?

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Re:What's Coming in Python 3.8 by n3k5 on Thursday July 18, 2019 @08:22AM (#20468990)

For contexts where the walrus is not allowed, see [0]. You'll find that it's generally possible to circumvent the restriction by parenthesising the expression. So yes,

    (x := 1)

is a valid (but poorly written) statement.

But while there are now two ways of doing assignment, I wonder how often people will actually encounter situations where it's difficult to figure out which choice is better.

[0] https://www.python.org/dev/peps/pep-0572/#exceptional-cases

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Re:What's Coming in Python 3.8 by Sohcahtoa82 on Thursday July 18, 2019 @12:56PM (#20471709)

Allowed, yes. But the PEP that introduced walrus operators says not to do it.

Every possible line of code has an alternate ugly way to write it. This isn't a valid criticism. Anyone who decides to start writing simple assignment statements like that deserves to be ridiculed for writing ugly code.

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Re:What's Coming in Python 3.8 by Scarblac on Thursday July 18, 2019 @03:08PM (#20472987)

Of course, and there's no reason to write such code.

I just dislike that the simple syntax rule "any expression can be used as a statement" now has an exception.

I haven't been able to think of scenarios where that might have consequences (code generation or refactoring tools?) but that doesn't say much as I'm not that smart.

Edit: having looked at the cases that are disallowed, they remind me of generator expressions. Those are usually written with parens, that can optionally be omitted in some cases. := is the same except they can be omitted in so many cases that it's easier to list the cases where they can't.

I think a generator expression used as a statement already requires the parens, even though they can be omitted e.g. as a single parameter of a function call. So that's probably ok then.

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