Is this valid ?

[Stef Mientki]

hello,

by accident I typed a double value test,
and to my surprise it seems to work.
Is this valid ?

a = 2
b = 2

a == b == 2

thanks,
Stef Mientki

[Mike Driscoll]

Re: Is this valid ?

On Mar 19, 4:18 pm, Stef Mientki <stef.mien...@g mail.comwrote:

hello,
>
by accident I typed a double value test,
and to my surprise it seems to work.
Is this valid ?
>
a = 2
b = 2
>
a == b == 2
>
thanks,
Stef Mientki

It sure looks that way...

See http://www.python.org/doc/2.3.5/ref/comparisons.html for more
info.

Mike

[Lie]

Re: Is this valid ?

On Mar 20, 4:18 am, Stef Mientki <stef.mien...@g mail.comwrote:

hello,
>
by accident I typed a double value test,
and to my surprise it seems to work.
Is this valid ?
>
a = 2
b = 2
>
a == b == 2
>
thanks,
Stef Mientki

a == b == 2
is equivalent to
a == b and b == 2
except that b is only evaluated once for the whole comparison

[Steven D'Aprano]

Re: Is this valid ?

On Thu, 20 Mar 2008 15:09:08 +0100, Rolf van de Krol 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.

Not at all. The Original Poster tried something, and it worked. There
were two alternatives:

(1) Writing a == b == 2 is valid.

(2) In the sixteen years that Python has been publicly available, with
tens of thousands or more developers using it, nobody had noticed that
Python had a bug in the compiler which incorrectly allowed a == b == 2
until Stef Mientki came along and discovered it.

Given those two alternatives, (2) would be very surprising indeed, and so
I think "of course" is well justified.

That Python allows chaining comparisons this way isn't really surprising.
That's a very natural thing to do. What's surprising is that other
languages *don't* allow chaining comparisons, but force you to write the
inefficient and (sometimes) confusing "(a == 2) and (b == 2)" instead.


--
Steven

[castironpi@gmail.com]

Re: Is this valid ?

On Mar 20, 6:06 pm, Steven D'Aprano <st...@REMOVE-THIS-
cybersource.com .auwrote:

On Thu, 20 Mar 2008 15:09:08 +0100, Rolf van de Krol 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.

>
Not at all. The Original Poster tried something, and it worked. There
were two alternatives:
>
(1) Writing a == b == 2 is valid.
>
(2) In the sixteen years that Python has been publicly available, with
tens of thousands or more developers using it, nobody had noticed that
Python had a bug in the compiler which incorrectly allowed a == b == 2
until Stef Mientki came along and discovered it.
>
Given those two alternatives, (2) would be very surprising indeed, and so
I think "of course" is well justified.
>
That Python allows chaining comparisons this way isn't really surprising.
That's a very natural thing to do. What's surprising is that other
languages *don't* allow chaining comparisons, but force you to write the
inefficient and (sometimes) confusing "(a == 2) and (b == 2)" instead.

You see a couple of occurrences in natural language-- I'm wondering
where the majority of NL settles.

>>a is a is a

True

Do we do math on booleans on some level or in some contexts? Maybe a
"with syntaxchangeA:" is in the future.

[Colin J. Williams]

Re: Is this valid ?

Lie wrote:

On Mar 20, 4:18 am, Stef Mientki <stef.mien...@g mail.comwrote:

>hello,
>>
>by accident I typed a double value test,
>and to my surprise it seems to work.
>Is this valid ?
>>
>a = 2
>b = 2
>>
>a == b == 2
>>
>thanks,
>Stef Mientki

>
a == b == 2
is equivalent to
a == b and b == 2
except that b is only evaluated once for the whole comparison

Yes - there seems to be unanimity.

Comparisons can be chained arbitrarily,
e.g., x < y <= z is equivalent to x < y
and y <= z, except that y is evaluated
only once (but in both cases z is not
evaluated at all when x < y is found to
be false).

Formally, if a, b, c, ..., y, z are
expressions and opa, opb, ..., opy are
comparison operators, then a opa b opb c
....y opy z is equivalent to a opa b and
b opb c and ... y opy z, except that
each expression is evaluated at most once.

Colin W.