Making Decisions with if
Run different code depending on whether a condition is true.
Programs often need to choose between actions. The if statement runs a block of code only when its condition is True.
Python
temperature = 34
if temperature > 30:
print("It is hot today.")
print("Drink plenty of water.")
print("Have a nice day!")Output
It is hot today. Drink plenty of water. Have a nice day!
The indented lines belong to the if. The last line is not indented, so it runs every time.
else and elif
Use else for "otherwise", and elif (short for "else if") to check more conditions in order. Python runs the first branch whose condition is true and skips the rest.
Python
marks = 72
if marks >= 90:
grade = "A"
elif marks >= 75:
grade = "B"
elif marks >= 60:
grade = "C"
else:
grade = "D"
print("Grade:", grade)Output
Grade: C
Comparing and combining
Comparison operators give back a bool: == (equal), != (not equal), <, >, <= and >=. Join conditions with and, or and not.
Python
age = 19
has_ticket = True
if age >= 18 and has_ticket:
print("You may enter.")
if not has_ticket or age < 18:
print("Sorry, no entry.")
else:
print("Enjoy the show!")Output
You may enter. Enjoy the show!