Komunitas Pelajar Indonesia

Looping Techniques Python

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