break and continue statements in Python

Loops Overview

Looping is a type of programming technique that allows a set of instructions or code to be repeated multiple times.

Python supports looping constructs through for and while loops.

seq = ['Python', 'Java', 'C++']

for i in seq:
    print(i)
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Output:
Python
Java
C++
[Finished in 0.010486217681318521s]

In the above example, we used a for loop to iterate through the elements of a list. The equivalent while loop is as shown below;

seq = ['Python', 'Java', 'C++']

i = 0
while i < len(seq):
    print(seq[i])
    i += 1
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Output:
Python
Java
C++
[Finished in 0.009532283060252666s]

The break statement

The break statement is used inside a loop to prematurely  terminate the loop. 

Once a break statement is encountered in either a for loop or a while loop, the  loop is immediately terminated and the program control resumes at the next statement following the loop.

The break statement is typically used together with a conditional block so that  when the condition is met, program execution will break out of the loop.

break with for loops

We can use the break statement inside a for loop to terminate the loop when a condition has been met.

seq = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

for i in seq:
    #define the condition
    if i == 5:
        break
    print(i)

print('after the loop')
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Output:
0
1
2
3
4
after the loop
[Finished in 0.009535283781588078s]

In the above example:

break with while loops

Just like in for loops, we can use the break statement inside of a while loop to prematurely terminate it.

seq = [ 1, 3, 5, 7, 9, 0, 2, 4, 6, 8]

i = 0
while i < len(seq):
    #define the condition
    if seq[i] % 2 ==  0:
        break
    print(seq[i])
    i += 1

print('after the loop')
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Output:
1
3
5
7
9
after the loop
[Finished in 0.009418158791959286s]

In the above example:

break with nested loops

A nested loop is when a loop appears inside the body of another loop. When a break statement is encountered in the inner loop,  only the inner loop is terminated and the outer loop continues to execute.

for i in range(5):

    #the inner loop
    for j in ['Python', 'Java', 'C++']:
        if j == 'C++':
            break
        print(j, end = ' ')
    print()
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Output:
Python Java 
Python Java 
Python Java 
Python Java 
Python Java 
[Finished in 0.009847722947597504s]

In the above example:

The continue statement

The break statement as we have seen makes the loop to terminate before the loop condition fails. The continue statement, on the other hand, makes the loop execution to skip  the current iteration and continue with the next iteration. 

Once the continue statement is encountered, the loop execution ignores the rest of the statements in the current iteration and immediately begins the next iterations.

Just like the break statement, the continue statement is also typically placed inside a conditional block so that it can execute only when certain conditions are met.

continue with for loop

We can use continue statement with for loops to skip the current loop iteration.

seq = [10, 20, 30, 40]

for i in seq:
    #the condition
    if i == 20:
        continue
    print(i)
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Output:
10
30
40
[Finished in 0.00993861723691225s]

In the above example:

continue with while loop 

We can also use the continue statement with a while loop.

data = ['Python', 'Java', 'C++', 'Ruby', 'PHP']

i = 0
while i < len(data):
    #the condition
    if data[i] == 'C++':
        i += 1
        continue

    print(data[i])
    i+=1
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Output:
Python
Java
Ruby
PHP
[Finished in 0.010710509028285742s]

Multiple continue statements

The continue statement can be executed more than once in a loop, this is unlike the break statement which can only be used once to exit a loop. 

#a for loop to print only the even numbers
for i in range(10):
    #the condition
    if i % 2 == 1:
         continue
    print(i)
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Output:
0
2
4
6
8
[Finished in 0.009601657278835773s]

In the above example, whenever an odd number is encountered, the continue statement gets executed making the loop to move to the next iteration without executing the print statement.