Getting Started with Python (Part 9): Using Loops and Iteration

Source: Dev.to

Using Loops and Iteration

In this article you’ll learn about loops, which allow you to repeat processing in Python.

Using the for Statement

By using a for statement, you can execute a process as many times as you like.

for variable in iterable:
    process

The for statement is often used together with lists (see the previous article about lists), and a common pattern is to process each value in a list one by one.

member = ["Maruko", "Tama", "Maruo"]
for person in member:
    print(person)
# Maruko
# Tama
# Maruo

When combined with the range() function, you can generate a sequence of numbers and process them in order.

range(end)                 # Numbers from 0 to end‑1
range(start, end)          # Numbers from start to end‑1
range(start, end, step)    # Numbers from start to end‑1, skipping by step

# Print numbers from 0 to 9
for n in range(10):
    print(n)
# 0
# 1
# 2
# …
# 7
# 8
# 9

Using the continue Statement

continue lets you skip the current iteration of a loop. When continue is executed, the remaining code in that iteration is skipped, and the loop moves on to the next iteration.

# Loop through numbers from 0 to 9
for n in range(10):
    if n % 2 == 0:
        continue  # Skip even numbers
    print(n)
# 1
# 3
# 5
# 7
# 9

Using the break Statement

break lets you stop a loop immediately. When break is executed, the entire loop is terminated.

# Loop through numbers from 0 to 9
for n in range(10):
    if n == 5:
        break  # Stop the loop when n is 5
    print(n)
# 0
# 1
# 2
# 3
# 4  <- The loop ends here

Using the while Statement

The while statement is another commonly used loop structure.

while condition:
    process

Here is a concrete example that calculates the sum of numbers from 0 to 9:

total = 0
n = 0
while n < 10:
    total += n
    n += 1
print(total)  # 45

Just like the for statement, while can also be used together with continue and break. However, be careful: if you make a mistake in the loop condition, you may end up with an infinite loop.

What’s Next?

Thank you for reading! In the next article we’ll learn about functions.

“Getting Started with Python (Part 7): Using Functions” – stay tuned! 🚀