YouTip

If Statements

Python uses if, elif, and else for conditional execution. Indentation defines code blocks.

# Basic if
age = 18
if age >= 18:
    print("Adult")

# if/else
if age >= 18:
    print("Adult")
else:
    print("Minor")

# if/elif/else
score = 85
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
else:
    grade = "F"

Comparison Operators

# ==  Equal
# !=  Not equal
# >   Greater than
# <   Less than
# >=  Greater or equal
# <=  Less or equal

x = 10
print(x == 10)   # True
print(x != 5)    # True
print(x > 5)     # True

Logical Operators

# and, or, not
age = 25
income = 50000

if age >= 18 and income >= 30000:
    print("Approved")

if age < 18 or income < 30000:
    print("Denied")

if not (age < 18):
    print("Adult")

For Loops

# Iterate over a list
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

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

for i in range(2, 6):    # 2, 3, 4, 5
    print(i)

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

# Enumerate
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

While Loops

# Basic while
count = 0
while count < 5:
    print(count)
    count += 1

# While with break
while True:
    user_input = input("Enter quit to exit: ")
    if user_input == "quit":
        break

# While with continue
count = 0
while count < 10:
    count += 1
    if count % 2 == 0:
        continue  # skip even numbers
    print(count)

List Comprehensions

# Create a list with a loop in one line
squares = [x**2 for x in range(10)]
# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# With condition
evens = [x for x in range(20) if x % 2 == 0]
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

# Nested
matrix = [[i*j for j in range(3)] for i in range(3)]

Summary

• Use if/elif/else for conditional logic
• for loops iterate over sequences, while loops repeat until condition is false
• break exits a loop, continue skips to the next iteration
• List comprehensions are a concise way to create lists