For Loops

A for loop repeats a block of code once for each item in a sequence. It is how you process every item in a list, every character in a word, or every number in a range, without copying and pasting code.

What You'll Learn

• Looping over lists and strings
• Generating number sequences with range()
• The accumulator pattern for building totals
• enumerate() for index-and-value

Looping Over a Sequence

The loop variable (fruit) takes each value in turn. Strings work the same way, one character at a time.

range()

range() generates numbers for you. range(5) counts 0 to 4; range(start, stop, step) gives you more control:

The Accumulator Pattern

Start a variable at zero, then add to it inside the loop. This is how you sum or count things:

enumerate(): Index and Value

When you need the position as well as the value, enumerate() gives you both:

You will use this in the to-do list project to print a numbered list.

Key Takeaways

• for item in sequence: repeats once per item
• range(n) counts 0 to n-1; range(start, stop, step) is flexible
• The accumulator pattern builds totals: start at 0, then += inside the loop
• enumerate() gives you the index and the value together