On Fri, Apr 27, 2018 at 1:38 AM, Gustavo Carneiro wrote:

On 26 April 2018 at 16:18, Chris Angelico wrote:

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On Thu, Apr 26, 2018 at 11:13 PM, Martin Teichmann wrote:

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Hi list,

when reading PEP 572 I actually liked it a lot - I think it's actually a cool idea. I think it's actually that cool an idea that it should be made the default way of doing an assignment, over time phasing out the good ole =.

This would have several benefits:

- people wouldn't have to worry about two different options - different things would have a different look: assignment is :=, keyword args is =, while comparison is ==. Especially beginners would benefit from this clarity.

in this case, for sure, we should make it possible to chain :=s, for example by making it bind right-to-left, so that a := b := 3 would be a := (b := 3)

I'm sorry if somebody brought that up already, but the discussion has grown so huge that I couldn't read through it entirely.

It has indeed grown huge. And in the interests of not growing it even huger, I'm not going to rehash the arguments against making := into the one and only operator, save to say one thing: there's no way that "x = 1" can be removed from the language any time soon, and by "soon" I mean even by the Yes Prime Minister definition, where "any day now", in strategic terms, meant "within the next half century".

In the interest of that, do you think := can be made illegal, by the grammar, if used outside an expression?

a = 1 # legal a := 1 # Syntax error if a := 1: # legal

No. Any expression may be used as a statement, so this isn't "outside an expression". ChrisA

On 4/26/2018 11:38 AM, Gustavo Carneiro wrote:

On Thu, Apr 26, 2018 at 11:13 PM, Martin Teichmann mailto:lkb.teichmann@gmail.com> wrote: > when reading PEP 572 I actually liked it a lot - I think it's actually > a cool idea. I think it's actually that cool an idea that it should be > made the default way of doing an assignment, over time phasing out the > good ole =.

Please no, I really, really appreciate not having to see add ':' all the time. Plus, it already has two other uses: end of header and dict key-item separator. Plus, see below.

In the interest of that, do you think := can be made illegal, by the grammar, if used outside an expression?

a = 1  # legal a := 1  # Syntax error if a := 1:  # legal

Please no. PEP 572 does not discuss top-level interactive assignments. But it should, because having two forms of assignment that lets one choose to echo or not is a plus. Sometimes one wants to see the result of an assignment. After

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a, b = 14387, 344

it would be nice to be able to write

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diff := a - b 14343

instead of

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diff = a - b diff 14343

I consider this a significant positive feature of the proposal. On the other hand, sometimes one does not want the see the result. A long result is often useless to view and may scroll previous results out of the window. A very long result may scroll previous results out of a finite console buffer altogether. (For Windows Command Prompt, the default is 300 lines, with a max of 9999.) And sometimes the result must not be printed. Tk text widgets (and hence IDLE's Shell) do not have a particular limit on the number of lines. On the other hands, long lines drasticly slow down a text widget, and a long enough line will freeze it. (This is supposed to be fixed in Tcl/Tk 8.7, now in a1 stage.) For instance, ">>> [None]*1000000" in IDLE freezes the process. -- Terry Jan Reedy