Python for else
Summary: in this tutorial, you’ll learn about the Python for else statement and how to use it effectively.
Introduction to the Python for else statement
In Python, the for statement can have an optional else clause, which you may not be familiar with especially if you’re coming from other languages such as Java or C#.
The following shows the syntax of the for statement with the else clause:
for item in iterables:
# process item
else:
# statementCode language: PHP (php)
In this syntax, the else clause will execute only if the loop runs normally. In other words, the else clause won’t execute if the loop encounters a break statement.
In addition, the else clause also executes when the iterables object has no item.
The following flowchart illustrates the for…else statement:
The else clause is quite useful in some cases if you know how to apply it effectively.
Python for else statement example
Suppose that you have a list of people, where each person is a dictionary that consists of name and age like this:
people = [{'name': 'John', 'age': 25},
{'name': 'Jane', 'age': 22},
{'name': 'Peter', 'age': 30},
{'name': 'Jenifer', 'age': 28}]Code language: JavaScript (javascript)
And you want to search for a person by name.
If the list contains the person, you want to display the information of that person. Otherwise, you want to show a message saying that the name is not found.
To do it, you may come up with a program like this:
people = [{'name': 'John', 'age': 25},
{'name': 'Jane', 'age': 22},
{'name': 'Peter', 'age': 30},
{'name': 'Jenifer', 'age': 28}]name = input('Enter a name:')
found = False
for person in people:
if person['name'] == name:
found = True
print(person)
break
if not found:
print(f'{name} not found!')
Code language: PHP (php)
How it works:
- First, prompt for a name by using the
input()function. - Then, set a flag (
found) toFalse. If the input name matches with a person on the list, set its value toTrue, show the person’s information and exit the loop by using thebreakstatement. - Finally, check the
foundflag and show a message.
The following runs a program with the name Peter and Maria:
1st run:
Enter a name:Peter
{'name': 'Peter', 'age': 30}Code language: Shell Session (shell)
2nd run:
Enter a name:Maria
Maria not found!Code language: Shell Session (shell)
It works perfectly fine.
However, if you use the for else statement, the program will be much shorter.
The following shows the new version of the program that uses the for else statement:
people = [{'name': 'John', 'age': 25},
{'name': 'Jane', 'age': 22},
{'name': 'Peter', 'age': 30},
{'name': 'Jenifer', 'age': 28}]name = input('Enter a name:')
for person in people:
if person['name'] == name:
print(person)
break
else:
print(f'{name} not found!')
Code language: PHP (php)
By using the for else statement, the program doesn’t need to use a flag and an if statement after the loop.
In this new program, if the input name matches a person on the list, it’ll show the person’s information and exit the loop by using the break statement.
When the loop encounters the break statement, the else clause won’t execute.
Summary
- Use Python
for elsestatement to execute a code block if the loop doesn’t encounter abreakstatement or if the iterables object has no item.