Python Loops: For, While, Break, and Continue

Loops let you run the same code over and over without rewriting it each time. Whether you need to count through numbers, process items in a list, or keep going until a condition changes, Python gives you for loops and while loops to handle it.

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How Does a For Loop Work in Python?

Let’s say you want to print the numbers 0 through 9. You could write ten print statements:

print(0)
print(1)
print(2)
# ... you get the idea
print(9)

A for loop saves you all that typing — especially if you wanted to do the same thing a thousand or a million times:

for i in range(0, 10):
    print(i)

The variable i takes on each value from 0 to 9, one at a time. In plain English:

1. Start with i equals 0
2. If i is greater than or equal to 10, exit the loop. Otherwise:
   • Print i to the console
   • Add 1 to i
   • Go back to step 2

The numbers in range(a, b) are inclusive of a and exclusive of b, so range(0, 10) includes 0 but not 10.

How Does range() Work in Python?

The range() function actually takes up to three parameters: range(start, stop, step).

The step parameter controls how much i changes each iteration. By default it’s 1, but you can change it:

for i in range(0, 10, 2):
    print(i)
# 0
# 2
# 4
# 6
# 8

You can even go backwards with a negative step:

for i in range(3, 0, -1):
    print(i)
# 3
# 2
# 1

This is useful any time you need to count down or iterate in reverse.

Why Does Whitespace Matter in Python Loops?

The body of a for loop must be indented, otherwise you’ll get a SyntaxError. Every line in the body needs to be indented the same way — the convention is 4 spaces. Pressing the <tab> key should insert 4 spaces automatically in most editors.

This is the same indentation rule that applies to if statements, functions, and every other block in Python. Whitespace matters.

How Do While Loops Work in Python?

A while loop keeps running as long as its condition is True:

while 1:
    print("1 evaluates to True")
# prints forever (infinite loop)

That example runs forever. Normally, a while loop’s condition involves a comparison that eventually becomes False:

num = 0
while num < 3:
    num += 1
    print(num)
# 1
# 2
# 3

The loop stops when num reaches 3 because 3 < 3 is False. Use a while loop when you don’t know ahead of time how many iterations you’ll need — for example, reading input until a user types “quit”, or processing data until a counter hits a limit.

What Does continue Do in a Python Loop?

The continue statement skips the rest of the current iteration and jumps straight to the next one. Whatever else was supposed to happen in that iteration gets skipped.

For example, if you want to skip negative numbers when calculating square roots:

for number in range(-5, 5):
    if number < 0:
        continue
    print(f"The square root of {number} is {number ** 0.5}")

The square root of 0 is 0.0
The square root of 1 is 1.0
The square root of 2 is 1.4142135623730951
The square root of 3 is 1.7320508075688772
The square root of 4 is 2.0

Using continue to avoid pointless work can make your code faster, especially when the loop body includes expensive computations.

What Does break Do in a Python Loop?

The break statement exits the loop entirely — not just the current iteration, but the whole thing:

for n in range(42):
    print(f"{n} * {n} = {n * n}")
    if n * n > 150:
        break

This would loop from 0 all the way to 41, but it exits early. Once n * n is greater than 150, the break executes and the loop stops. The last line printed is 13 * 13 = 169.

break is handy when you’re searching for something and want to stop as soon as you find it, rather than continuing through the rest of the sequence.

What Should You Learn After Python Loops?

Loops and conditionals together give you full control over your program’s flow. The next step is usually lists — loops and lists go hand in hand since you’ll often loop over collections of data.

If you want to keep going through the full Python curriculum with hands-on exercises, check out the Learn to Code in Python course on Boot.dev.