Loops are used to repetitively execute a sequence of statements while changing a variable from iteration to iteration. This variable is called the index variable. It is successively assigned to the elements of a list, (refer to Chapter 9, Iterating) :
L = [1, 2, 10]
for s in L:
print(s * 2) # output: 2 4 20The part to be repeated in the for loop has to be properly indented:
for elt in my_list:
do_something
something_else
print("loop finished") # outside the for blockOne typical use of a for loop is to repeat a certain task a fixed number of times:
n = 30 for iteration in range(n): do_something # this gets executed n times
The for statement has two important keywords: break and else. break quits the for loop even if the list we are iterating is not exhausted:
for x in x_values: if x > threshold: break print(x)
The finalizing else checks whether the for loop was broken with the break keyword. If it was not broken, the block following the else keyword is executed:
for x in x_values:
if x > threshold:
break
else:
print("all the x are below the threshold")