Week 1 • Tuesday

Block 4: for Loops & range()

Repeat actions with for loops and range().

Concepts

for item in iterable: pattern
range(start, stop, step)
Loop over lists and strings
Accumulator pattern with a variable

Code Examples

range() and for loop

for i in range(5):
    print(i)  # 0,1,2,3,4
for i in range(2, 10, 2):
    print(i)  # 2,4,6,8

Accumulator pattern

numbers = [1, 2, 3, 4, 5]
total = 0
for n in numbers:
    total += n
print(total)  # 15

Exercise

Implement FizzBuzz from 1 to 50. Sum all even numbers from 1 to 100 using a loop.

Solution

# FizzBuzz
for i in range(1, 51):
    if i % 15 == 0: print('FizzBuzz')
    elif i % 3 == 0: print('Fizz')
    elif i % 5 == 0: print('Buzz')
    else: print(i)

# Sum evens 1-100
total = 0
for n in range(2, 101, 2):
    total += n
print('Sum of evens:', total)  # 2550

Practice Problems

Problem 1: Print the first 10 square numbers (1, 4, 9, 16, ...)

Hint: for i in range(1, 11): print(i**2)

Problem 2: Count how many vowels are in the string 'hello world'

Hint: Loop over chars, check if in 'aeiou'

Application

Loops are fundamental for iterating over datasets, processing batches, and running simulations.

Case Study

A data pipeline loops over 1000 CSV files, reads each, cleans it, and appends to a master DataFrame. The accumulator pattern builds the final dataset.

Homework

What is the difference between range(5) and range(1,6)? Show with code.