When looping through dictionaries, the key and corresponding value can be retrieved at the same time using the iteritems() method.

>>> knights = {‘gallahad’: ‘pure’, ‘robin’: ‘brave’}
>>> for k, v in knights.iteritems():
…     print k, ‘the’, v
…
gallahad the pure
robin the brave

When looping through a sequence, the position index and corresponding value can be retrieved at the same time using the enumerate() function.

>>> for i, v in enumerate(['tic', 'tac', 'toe']):
…     print i, v
…
0 tic
1 tac
2 toe

To loop over two or more sequences at the same time, the entries can be paired with the zip() function.

>>> questions = ['name', 'quest', 'favorite color']
>>> answers = ['lancelot', 'the holy grail', 'blue']
>>> for q, a in zip(questions, answers):
…     print ‘What is your %s?  It is %s.’ % (q, a)
…
What is your name?  It is lancelot.
What is your quest?  It is the holy grail.
What is your favorite color?  It is blue.

To loop over a sequence in reverse, first specify the sequence in a forward direction and then call the reversed() function.

>>> for i in reversed(xrange(1,10,2)):
…     print i
…
9
7
5
3
1

To loop over a sequence in sorted order, use the sorted() function which returns a new sorted list while leaving the source unaltered.

>>> basket = ['apple', 'orange', 'apple', 'pear',
'orange', 'banana']
>>> for f in sorted(set(basket)):
…     print f
…
apple
banana
orange
pear

sumber : http://www.network-theory.co.uk/docs/pytut/LoopingTechniques.html

syntax untuk while loop:

while (expression)
{
code to
execute;
}

contoh while loop yang menghitung sampai 10

script————-

$num = 1;

while ($num <= 10){
print “Number is $num
\n”;
$num++;
}

print ‘Done.’;
?>

script————-

menghasilkan:

Number is 1
Number is 2
Number is 3
Number is 4
Number is 5
Number is 6
Number is 7
Number is 8
Number is 9
Number is 10
Done.

script nya akan me-loop sampai 10 dan script $num++ bertambah 1

2. For Loops
syntax untuk For Loops adalah

for (initialization expression; test expression; modification expression){
code that is executed;
}

contoh script untuk for loop:

script————-

for ($num = 1; $num <= 10; $num++) {
print “Number is $num
\n”;
}
?>

script————-

menghasilkan:

Number is 1
Number is 2
Number is 3
Number is 4
Number is 5
Number is 6
Number is 7
Number is 8
Number is 9
Number is 10

3. Menghentikan sebuah Loop

contoh Menghentikan sebuah Loop untuk menghindari Loop:

script————-

$counter = -3;

for (; $counter < 10; $counter++){
// Check for division by zero
if ($counter == 0){
echo “Stopping to avoid zero.”;
break;
}

echo “100/$counter
“;
}

?>

script————-

menghasilkan:

100/-3
100/-2
100/-1
Stopping to avoid division by zero.

*dia akan loop sampai fungsi if dan karena ada script break, maka proses akan berhenti
*script ini suatu saat akan berguna “Trust me”

4. continue Statements

penggunaan continue selain break

script————-

$counter =- 3;

for (; $counter < 10; $counter++){
// Check for division by zero
if ($counter == 0){
echo “Skipping to avoid zero.
“;
continue;
}

echo “100/$counter
“;
}

?>

script————-

menghasilkan:

100/-3
100/-2
100/-1
Skipping to avoid zero.
100/1
100/2
100/3
100/4
100/5
100/6
100/7
100/8
100/9

*dia akan loop sampai fungsi if dan karena ada script continue, maka proses akan berhenti mengganti angka 0 menjadi
Skipping to avoid zero, lalu looping akan di lanjutkan kembali