09 How to Use Operator and IF statement in Python + Tips (Video in Khmer)

Hello friend! 👋 Program need to make decision. Example: "If age is 18 or more, can vote."

In this post, I show you operators and if statement in Python. Easy and short. 🐍

⚖️ Comparison Operators

Compare two value. Result is always True or False.

Operator	Mean	Example	Result
`==`	Equal	`5 == 5`	`True`
`!=`	Not equal	`5 != 3`	`True`
`>`	Bigger than	`5 > 3`	`True`
`<`	Smaller than	`5 < 3`	`False`
`>=`	Bigger or equal	`5 >= 5`	`True`
`<=`	Smaller or equal	`3 <= 2`	`False`

age = 20

print(age == 20)   # True
print(age != 20)   # False
print(age > 18)    # True
print(age <= 18)   # False

Careful: = put value into variable. == compare value.

x = 5      # put 5 into x
x == 5     # check x is 5 or not

🎥 Video: Using Comparison Operators in Python (Khmer)

🔗 Logical Operators

Join many condition together.

Operator	Mean
`and`	Both must be `True`
`or`	One is `True` is enough
`not`	Change `True` to `False`

age = 20
has_id = True

print(age >= 18 and has_id)   # True
print(age < 18 or has_id)     # True
print(not has_id)             # False

✅ if Statement

Run code only if condition is True.

age = 20

if age >= 18:
    print("You can vote")

print("Done")

Remember: put : after condition, and indent the code inside (4 space).

↔️ if ... else

Two way: one for True, one for False.

age = 15

if age >= 18:
    print("Adult")
else:
    print("Child")

Output:

Child

🪜 if ... elif ... else

Many way. Python check from top to bottom. Stop at first True.

score = 85

if score >= 90:
    print("Grade A")
elif score >= 80:
    print("Grade B")
elif score >= 70:
    print("Grade C")
else:
    print("Fail")

Output:

Grade B

🎥 Video: Using IF and IF ELIF ELSE (Khmer)

🧪 More Example

Check with user input

age = int(input("Enter age: "))

if age >= 18 and age <= 60:
    print("Working age")
elif age > 60:
    print("Retired")
else:
    print("Student")

Short way: chain compare

age = 25

print(18 <= age <= 60)   # True

Check list and string

fruits = ["apple", "banana"]

if "apple" in fruits:
    print("We have apple")

name = ""
if not name:
    print("Name is empty")

One line if (ternary)

age = 20
status = "Adult" if age >= 18 else "Child"
print(status)   # Adult

❌ Common Error

Use = instead of ==:

if age = 18:    # SyntaxError
    print("Yes")

Fix: if age == 18:

Forget :

if age >= 18
    print("Adult")    # SyntaxError

Forget indent:

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

Wrong order in elif:

score = 95

if score >= 70:
    print("Grade C")   # run this, wrong!
elif score >= 90:
    print("Grade A")   # never run

Fix: check biggest first.

💡 Tips

Use == to compare, = to save value.
Always put : after if, elif, else.
Use 4 space for indent. Same block must have same space.
In elif, put the biggest or most special condition first.
Use and, or instead of many nested if.
Use 18 <= age <= 60 — short and easy to read.
Empty string, empty list, 0 and None are False. Use if not name: to check.
Need compare string? Use .lower(): if answer.lower() == "yes":
input() give string. Use int() before compare number.

❓ Any Question?

Tell us in comment below! 👇

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