Python for Loop

---

Python for loops repeat code. You can use it to repeat one or more lines of code.

• Python for loop is used to iterate over a sequence of items
• The for loop has the reserved keyword: for
• The for-loop code is run for each element of the sequence
• You can end the for loop using the break statement
• You can use continue statement to skip the the code in the for loop for an element
• Python behaves more like an iterator
• For loops can iterate over Tuple, List, Set and String. They are all Python sequences.
• You can have nested for loops to iterate over a sequence of sequences

Related course: Complete Python Programming Course & Exercises

Python for Loop Syntax

The Python for loop syntax is simple for x in y:. The in operator is used to iterate over the elements in the sequence.

for element in sequence:
    # code block

Python for Loop Examples

String

A for loop can loop over a string. It goes over a string character by character. The basic example below will output each character once.

 for x in "hello":
     print(x)

This makes no difference if you have a sentence, so the following will work too:

 s = "Hello world, moon, universe"
 for x in s:
     print(f"char is {x}")

Tuple

A for loop can loop over a tuple. Every element of the tuple is in each reptition. For loops can be inside functions, in the example below the for loop is in the function lower_case().

def lower_case(my_tuple):
    temp_list = []
    for item in my_tuple:
        temp_list.append(str(item).lower())
    return tuple(temp_list)


fruits = ("Apple", "Orange", "LEMON")
fruits_new = lower_case(fruits)
print(fruits_new)

List

A for loop can loop over a list, this is another type of sequence. Like tulpe it goes over every element once.

magicians = ['alice', 'david', 'carolina']
for magician in magicians:
    print(magician.title() + ", that was a great trick!")
    print("I can't wait to see your next trick, " + magician.title() + ".\n")

Set

A for loop can loop over a set. It doesn't matter how many elements the set has. The set is created by calling the function set().

cities = set()
cities.add("Paris")
cities.add("Barcelona")
cities.add("Milano")
cities.add("Oslo")
cities.add("Bern")

for city in cities:
    print(city)

Dictionary

A for loop can loop over a dictionary (A dictionary is a collection of key-value pairs). To loop over a dictionary you can use .items() and grab the keys and values together.

my_dict = {"1": "Cat", "2": "Koala", "3": "Mouse"}

for k, v in my_dict.items():
    print(f'Key={k}, Value={v}')

Using break Statement to Exit for Loop

You can use the reserved keyword break to exit a loop. This exits the loop and continues the rest of the program. In generally you should avoid using break in loops.

messages = ["Aloha", "Hallo", "Exit", "Hasta la vista", "Sayonara"]

for msg in messages:
    if msg == "Exit":
        break;
    print(f'Processing {msg}')

Python for Loop with continue Statement

The continue statement can be used to skip a cycle of the loop. If Python sees continue, it will skip the current cycle and continue in the next cycle.

ints = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

# process only odd numbers
for i in ints:
    if i % 2 == 0:
        continue
    print(f'Processing {i}')

Python for loop with range() function

Range generates a list of numbers, this can be used to loop over numbers. This is practical when you want to loop over a fixed amount of numbers.

for i in range(5):
    print("Processing for loop:", i)

for Loop with else statement

The else keyword can be used in a loop. The program will go in the else clause when the loop has finished.

databases = ("PostgreSQL", "SQL Server","MySQL", "Oracle")

for db in databases:
    print(f'Database is {db}')
else:
    print("Finished processing list.")

Nested for Loops in Python

You can have nested loops (with tuples or lists). A nested loop is a loop inside a loop. This allows you to combine several collections.

list_tuples = [("Lemon", "Berry", "Melon"), ("Pear", "Guava", "Strawberry")]

for t_fruits in list_tuples:
    for fruit in t_fruits:
        print(fruit)

Reverse Iteration using for Loop and reversed() function

The function reversed() turns a collection in reverse order. If you want to loop over a collection in reverse order, just call the reversed() function.

numbers = (1, 2, 3, 4, 5)

for n in reversed(numbers):
    print(n)