for(each) element aliasing

[Matija Papec]

I know how to alter the list via list indicies but I would like to know if
there is posibility to write in Python something like:

my @arr = 1..3;
for my $element (@arr) {
$element *= 2;
}
print "@arr\n";

and get the result
-------
2 4 6
--
Matija

[Andreas Lobinger]

Aloha,

Matija Papec wrote:

my @arr = 1..3;
for my $element (@arr) {
$element *= 2;
}
print "@arr\n";
2 4 6

arr = [1,2,3]
print [element*2 for element in arr]

[2, 4, 6]

Wishing a happy day
LOBI

[F. Petitjean]

On Mon, 22 Nov 2004 17:21:26 +0100, Matija Papec <mp****@yahoo.com> wrote:

I know how to alter the list via list indicies but I would like to know if
there is posibility to write in Python something like:

my @arr = 1..3;
for my $element (@arr) {
$element *= 2;
}
print "@arr\n";
For instance :
arr = 1, 2, 3 # range(1, 4)
arr = [ element*2 for element in arr ]
print arr # [2, 4, 6] it is a list
for element in arr:
print element, # note the comma
print # useful if not in interactive mode only
Read the documentation about "list comprehension"
and get the result
-------
2 4 6

[Will McGugan]

Matija Papec wrote:

I know how to alter the list via list indicies but I would like to know if
there is posibility to write in Python something like:

my @arr = 1..3;
for my $element (@arr) {
$element *= 2;
}
print "@arr\n";

and get the result
-------
2 4 6

Something like this?

arr= range(1,4)
for index, value in enumerate( arr):
arr[index]*= 2

print arr

Regards,

Will McGugan

[Reinhold Birkenfeld]

Will McGugan wrote:

Matija Papec wrote:

I know how to alter the list via list indicies but I would like to know if
there is posibility to write in Python something like:

my @arr = 1..3;
for my $element (@arr) {
$element *= 2;
}
print "@arr\n";

and get the result
-------
2 4 6

Something like this?

arr= range(1,4)
for index, value in enumerate( arr):
arr[index]*= 2

But for this you won't need enumerate:

One of
for index in range(len(arr)):
for index in xrange(len(arr)):

is sufficient.

Reinhold

--
[Windows ist wie] die Bahn: Man muss sich um nichts kuemmern, zahlt fuer
jede Kleinigkeit einen Aufpreis, der Service ist mies, Fremde koennen
jederzeit einsteigen, es ist unflexibel und zu allen anderen Verkehrs-
mitteln inkompatibel. -- Florian Diesch in dcoulm

[Istvan Albert]

Reinhold Birkenfeld wrote:

But for this you won't need enumerate:
for index in range(len(arr)):

Isn't the range(len(arr)) construct somewhat of an
contraption? It has become a recognizable pattern
of course but that was by necessity rather than
correctness.

Istvan.

[Matija Papec]

X-Ftn-To: Jp Calderone

Jp Calderone <ex*****@divmod.com> wrote:

-------
2 4 6

No. Integers in Python are immutable. For lists of other things, mutation in-place (similar to the above example) is possible, but for integers and other immutable types, it is not. You may be interested in list comprehensions, though:

arr = range(1, 4)
arr[:] = [a * 2 for a in arr]
print arr

I guess this works like "map" but "for" is more idimatic.
Thank you all for so quick responses. :)
--
Matija

[Reinhold Birkenfeld]

Matija Papec wrote:

X-Ftn-To: Jp Calderone

Jp Calderone <ex*****@divmod.com> wrote:

-------
2 4 6

No. Integers in Python are immutable. For lists of other things, mutation in-place (similar to the above example) is possible, but for integers and other immutable types, it is not. You may be interested in list comprehensions, though:

arr = range(1, 4)
arr[:] = [a * 2 for a in arr]
print arr

I guess this works like "map" but "for" is more idimatic.

Yes. List comprehensions are elegant (and fast) expressions you would
otherwise construct with map() and filter().

Reinhold

--
[Windows ist wie] die Bahn: Man muss sich um nichts kuemmern, zahlt fuer
jede Kleinigkeit einen Aufpreis, der Service ist mies, Fremde koennen
jederzeit einsteigen, es ist unflexibel und zu allen anderen Verkehrs-
mitteln inkompatibel. -- Florian Diesch in dcoulm

[Matija Papec]

>> arr[:] = [a * 2 for a in arr]

print arr

I guess this works like "map" but "for" is more idimatic.

idiomatic
--
Matija