DaveM wrote:
On Sun, 27 Jul 2008 05:24:36 -0700 (PDT), alex23 <[EMAIL PROTECTED]> wrote:
On Jul 27, 10:13 pm, ssecorp <[EMAIL PROTECTED]> wrote:
I have seen somewhere that you can write something like:
x*x if x>10
but exactly that doesn't work and I can't get any variation to work.
It's called a ternary operator. The format is:
<label> = <true-value> if <condition> else <false-value>
I've seen the PERL saying/motto/boast, "There's more than one way to do it"
derided on more than one occasion on this group so what's the reason for
this additional way to put an if else statement on one line? Are "and" and
"or" constructions to produce the same effect not supported for this use?
The "and" and "or" construct which is equivalent to the ternary operator
is quite convoluted and looks nothing like a conditional computation:
(C and [A] or [B])[0]
This is inefficient, and nearly unreadable, which makes the highly
useful ternary operator worthy of a syntactical construct.
The [A], [B] and [0] parts are absolutely necessary in the general case
where A can have values that Python would consider equivalent to False.
If you know A will never be equivalent to False then you can use just this:
C and A or B
Gary Herron
And while I'm on my high horse, I'd like to bring up list concatenations. I
recently needed to concatenate 5 lists, which doesn't sound a particularly
rare requirement to me. My first attempt was a straightforward loop
extending an empty list. That worked fine but looked like an awful bulky
solution. Afterwards I tried various formulae using "reduce" , falling foul
of the "=" catch on one occasion. Now I'm not a professional programmer, so
there may be good reasons for a single object to have multiple names in a
program, but it sounds like a recipe for disaster to me. Getting back to the
list concatenation, I finally found the itertools.chain command which is the
most compact and fastest (or second fastest by a trivial amount, I can't
remember which). Along the way, I must have tried/used half a dozen methods,
...which brings me back my initial PERL comment. There's more than one way
to do it in Python, too.
DaveM
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