PySchools Python Quick Reference Guide

Repetitions with for loops

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Repetitions with for loops

In Python, for loop is usually used with the range() or the xrange() function. To print a number from 1 to 10:

for i in range(1, 11):
    print i

#output:
1
2
3
4
5
6
7
8
9
10

Using for loop with List

for loop is usually used to traverse the elements in a list. For example, to add all the numbers in a list:

num_list = [2, 5, 9, 1, 4]

total = 0
for num in num_list:
    total += num

print "Total: ", total

#ouput:
'Total: 21'

More on the range() function

The range(start, end, step) function takes in 3 arguments and generate a list of number based on these arguments. Some examples are shown below:

>>> range(10) # by default, start = 0, step = 1, last number: 10 is not included
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> range(5, 10) # by default, step = 1
[5, 6, 7, 8, 9]
>>>> range(2, 10, 2)
[2, 4, 6, 8]

The code belows show a comparison of the for loop in Java and Python.

# Java code, printing 1, 3, 5, 7, 9
for (int i = 1; i < 10; i+=2)
    System.out.println(i);

# Python code, printing 1, 3, 5, 7, 9
for i in range(1, 10, 2):
    print i

See also

Ready for some practice? Test your understanding at PySchools: For Loops.

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