การวนซ้ำด้วย for และ range

When you want to visit each value in turn, reach for a for loop. It pulls one item at a time and runs the body for each. 🚶

Write for, a loop variable, the word in, something to walk over, then a colon and an indented block.

To loop a fixed number of times, pair for with range. range(n) yields 0 up to but not including n.

This catches beginners: range(5) gives 0, 1, 2, 3, 4. The end value is excluded, so you get exactly five numbers.

Give range two values to set a start and end. range(2, 5) walks 2, 3, 4, beginning where you tell it.

A third value sets the step between numbers. range(0, 10, 2) yields the even numbers 0, 2, 4, 6, 8.

A negative step lets range go backward. range(3, 0, -1) produces 3, 2, 1, perfect for a simple countdown.

for works on collections too. Iterating a List hands you each element directly, so you rarely need an index.

If you do need positions, loop over range(len(items)) and use the index to reach into the collection.

Just like while, a for loop can build a total. Initialize before the loop, then add inside the body each pass.

Use for with range when the number of passes is known up front. It is clearer and harder to break than a manual while.

You write for i in range(5). Which exact sequence of numbers does i take across the loop?

A for loop visits each item, and range generates numbers with start, end, and step. Remember the end value is excluded. 🎯