Python for Loops and while Loops Explained with Examples (range, break, continue)
P6.1 How a for Loop Works in Python
Why. You have 500 invoices and must check each one. Writing 500 lines is impossible. A loop writes it once and repeats it.
What. for item in collection: takes each item one by one and runs the indented block for it.
How.
Write a for loop
- Write
for, a name for one item,in, the list, and a colon. - Indent the work to repeat.
- Use the item name inside the block.
Worked example A — Print each item.
Step 1 — What we do. A store in Kraków has three branches.
Step 2 — Type and run this code.
branches = ["Old Town", "Kazimierz", "Podgorze"]
for b in branches:
print("Branch:", b)
Step 3 — Output you should see.
Branch: Old Town
Branch: Kazimierz
Branch: Podgorze
Step 4 — What it means. The block ran 3 times, once per branch. b holds the current item.
Worked example B — Add up with a loop.
Step 1 — What we do. We total daily sales manually to see how sum works inside.
Step 2 — Type and run this code.
sales = [1200, 950, 1430]
total = 0
for s in sales:
total = total + s
print(total)
Step 3 — Output you should see.
3580
Step 4 — What it means. Start at 0, add each value. The result 3580 is the same as sum(sales).
Worked example C — Loop over a string.
Step 1 — What we do. We count the digits in a phone number field.
Step 2 — Type and run this code.
phone = "+44 20 7946 0958"
digits = 0
for ch in phone:
if ch.isdigit():
digits += 1
print(digits)
Step 3 — Output you should see.
12
Step 4 — What it means. A string is a sequence of characters, so a loop visits each one. += 1 is short for "add 1".
Python next to other languages — loop over a list. You do not need to learn these other languages. This only shows why Python is easier to read.
| Language | Code |
|---|---|
| Python | for b in branches: print(b) |
| Java | for (String b : branches) { System.out.println(b); } |
| JavaScript | for (const b of branches) { console.log(b); } |
| Go | for _, b := range branches { fmt.Println(b) } |
Ravindra Bagale's Tip
Name the loop variable as the singular of the list: for order in orders, for city in cities. The code reads like English.
Ravindra Bagale's Tip – मराठी
Loop variable ला list चं एकवचनी नाव द्या: for order in orders, for city in cities. Code इंग्रजी सारखा वाचता येतो.
Ravindra Bagale's Tip – हिंदी
Loop variable का नाम list का एकवचन रखो: for order in orders, for city in cities. Code अंग्रेज़ी जैसा पढ़ा जाता है.