For Loop

range() Function

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     	
						

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 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:

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

# by default, step = 1
>>> range(5, 10) 
[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
						

Code Snippets

This section will contain some code snippets to show some practical use of the topic that you have learnt.

# Printing patterns
# -------------------
+ 
+ + 
+ + + 
+ + + + 
+ + + + + 

for i in range(1, 6):
    print i * "+ "
    
# Printing more patterns
# ----------------------
@ @ @ @ @ 
+ + + + + 
@ @ @ @ @ 
+ + + + + 
@ @ @ @ @ 

for i in range(1, 6):
    if i % 2 == 0:
        print 5 * "+ "
    else:
        print 5 * "@ "