On 2021-10-03 10:39:38 +1100, Chris Angelico wrote: > Using assignment expressions in lambda functions sometimes works, but > sometimes doesn't.
> ... return lambda x: (x, x := 2, x)
syntax ok
> return lambda: n := 1
syntax error
> ... return lambda: (n := 1)
syntax ok
> return (lambda: n := 1)
syntax error
> ... return (lambda: (n := 1)), (lambda: n)
syntax ok, but doesn't assign
...
> What's going on here?
I think it's the parentheses:
The right side of the lambda is defined as an «expression», not an an
«assignment_expression», and there is no direct derivation from one to
the other in the grammar. So you can't put an «assignment_expression» there
directly. But if you put it in parentheses, it becomes a «starred_item»
which is a «starred_expression» which is then part of the «parenth_form»
which is an «enclosure» which is an «atom» which is (through several
more steps) an «expression» which can be used on the right side of a
lambda.
hp
--
_ | Peter J. Holzer | Story must make more sense than reality.
|_|_) | |
| | | h...@hjp.at | -- Charles Stross, "Creative writing
__/ | http://www.hjp.at/ | challenge!"
signature.asc
Description: PGP signature
-- https://mail.python.org/mailman/listinfo/python-list
