Python Tutorial, Release 3.9.5 5.6. Looping Techniques 39 >>> questions =['name','quest','favorite color'] >>> answers =['lancelot ','the holy grail','blue'] >>> for q, a in zip (questions, answers): ... print('What is your {0} ? It is {1} .'.format(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(range(1,10 ,2)): ... print(i) ... 9 7 5 3 1 >>> basket =['apple','orange','apple','pear','orange','banana'] >>> for i in sorted(basket): ... print(i) ... apple apple banana orange orange pear >>> basket =['apple','orange','apple','pear','orange','banana'] >>> for f in sorted(set(basket)): ... print(f) ... apple banana orange pear >>> import math >>> raw_data=[56.2 ,float('NaN '),51.7 ,55.3 ,52.5 ,float('NaN '),47.8 ] >>> filtered_data=[] >>> for value in raw_data: ... if not math.isnan(value): ... filtered_data .append(value) ... >>> filtered_data [56.2, 51.7, 55.3, 52.5, 47.8] It is sometimes tempting to change a list while you are looping over it; however, it is often simpler and safer to create a new list instead. Using$_{set()}$ on a sequence eliminates duplicate elements. The use of$_{sorted()}$ in combination with$_{set()}$ over a sequence is an idiomatic way to loop over unique elements of the sequence in sorted order. To loop over a sequence in sorted order, use the$_{sorted()}$ function which returns a new sorted list while leaving the source unaltered.