Is this valid ?

[John Machin]

On Mar 21, 1:09 am, Rolf van de Krol <pyt... at rolfvandekrol.nl> wrote:
> John Machin wrote:
> > Of course. You can chain comparisons as much as you like and is
> > (semi-)sensible, e.g.
>
> Hmm, 'of course' is not the correct word for it.

'Of course' was short for: Given alternative hypotheses H0 = "Python
feature" and H1 = "bug in Python compiler", one's instinct would be go
with H0 if a snap decision were required without time to refer to the
docs.

> Although the Stef
> Mientki would probably be able to find it in the documentation it is not
> as simple as you might think.
> Most languages interpret a == b == 2 as (a == b) == 2, or throw an error
> because this syntax is not valid.

Indeed, some languages do ludicrous things with precedence of
relational operators. A compiler when faced with something like:
    a == b and c == d
has at least two choices:
(1) (a == b) and (c == d) # seems rather useful
(2) (a == (b and c)) == d
which doesn't seem very useful at all. Pascal makes choice (2), which
is valid syntax only if b and c are booleans and if comparisons of
booleans are allowed (and IIRC Pascal didn't allow this).

> The fact that python understand the
> obvious meaning of this code, is quite unique to Python, as far as I know.

Indeed, Python isn't "some/most languages", which is why we're here.