On 5/10/2018 9:53 AM, Guido van Rossum wrote:
On Thu, May 10, 2018 at 3:32 AM, Terry Reedy
<tjre...@udel.edu
<mailto:tjre...@udel.edu>> wrote:
On 5/9/2018 11:33 PM, Guido van Rossum wrote:
I now think that the best way out is to rule `:=` in the top
level expression of an expression statement completely
I would like to be able to interactively enter
>>> a: = f(2,4)
to have 'a' echoed as well as bound.
I hope that's a typo (the can be no space between `:` and `=`, since
`:=` is a single token, just like `<=').
a := f(2,4) # corrected ;-)
We *could* make this work while still ruling out the ambiguous cases
(which involve top-level commas on either side of the assignment
expression).
OTOH I worry that this particular feature would cause `:=` to become
part of many a teacher's bag of tricks to show off,
until someone tries a := [0]*10000000
exposing users to it way too early for any curriculum, > and it might then
elicit complaints that
def f():
... a := 5
...
f()
doesn't print `5`.
Although the reason the same as for any expression, I can believe that
people will see it as different. A bare assignment expression *looks*
like a statement in a way that other expressions do not.
So all in all I'm not sure I think this is important enough to support,
and the rule "Use `:=` in expressions, not as a top level assignment"
seems easier to explain and understand.
--
Terry Jan Reedy
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