range-and-enumerate.md

Python by Example: Range and Enumerate

range() produces a sequence of integers without building a list in memory—it's lazy and efficient. Use it when you need to loop a fixed number of times or generate indices. enumerate() pairs each element with its index, so you get both when iterating. Both work in for loops.

What you'll learn:

• range(stop), range(start, stop), range(start, stop, step)
• enumerate(iterable, start=0) for index-value pairs

# range(stop) — 0 to stop-1
for i in range(5):
    print(i, end=" ")
print()

# range(start, stop)
for i in range(2, 6):
    print(i, end=" ")
print()

# range(start, stop, step)
for i in range(0, 10, 2):
    print(i, end=" ")
print()

# enumerate: index and value
fruits = ["apple", "banana", "cherry"]
for i, fruit in enumerate(fruits):
    print(f"{i}: {fruit}")

# Start counting from 1
for i, fruit in enumerate(fruits, start=1):
    print(f"{i}. {fruit}")

range(5) yields 0, 1, 2, 3, 4—stop is exclusive. enumerate(fruits) yields (0, "apple"), (1, "banana"), (2, "cherry"). Use start=1 when you want 1-based numbering for display.

To run this program:

$ python source/range-and-enumerate.py
0 1 2 3 4
2 3 4 5
0 2 4 6 8
0: apple
1: banana
2: cherry
1. apple
2. banana
3. cherry

Tip: Prefer for i, item in enumerate(items): over for i in range(len(items)): when you need the index—it's cleaner and less error-prone.

Try it: Use enumerate to print a numbered list of your favorite colors.

Source: range-and-enumerate.py

Next: Comprehensions