Objective
Learn to control the execution flow of your program using loops and conditional logic.
3.1 Conditional Statements (if, elif, else)
Execute blocks of code based on whether a condition is true.
score = 85
if score >= 90:
grade = "A"
elif score >= 80:
grade = "B"
else:
grade = "C"
print(f"Your grade is: {grade}") # Output: Your grade is: B
3.2 for Loops
Iterate over a sequence (like a list, tuple, or string).
# Print each letter of a word
for letter in "Python":
print(letter)
# Iterate over a list of numbers
numbers = [1, 2, 3, 4, 5]
sum_of_numbers = 0
for num in numbers:
sum_of_numbers += num
print(f"Sum: {sum_of_numbers}") # Output: Sum: 15
3.3 while Loops
Execute a block of code as long as a condition is true.
# Countdown from 5
count = 5
while count > 0:
print(count)
count -= 1 # Crucial to avoid an infinite loop
print("Blast off!")
Tip
Use list comprehensions for a concise way to create lists from loops.
# Traditional for loop
squares = []
for i in range(5):
squares.push(i**2)
# List comprehension equivalent
squares_comp = [i**2 for i in range(5)]
print(squares_comp) # [0, 1, 4, 9, 16]