Variable assignment in Python

Introduction

Variable assignment lets you store information to use later in your program. It helps keep track of values like numbers or words.

When you want to remember a user's name after they type it.

When you need to store a number to use in calculations.

When you want to save a message to show on the screen.

When you want to keep track of a score in a game.

When you want to hold temporary data while your program runs.

Syntax

Python

variable_name = value

The = sign means 'store this value in the variable'.

Variable names should start with a letter or underscore and have no spaces.

Examples

This stores the word "Alice" in the variable called name.

Python

name = "Alice"

This stores the number 30 in the variable called age.

Python

age = 30

This stores a decimal number (float) 23.5 in temperature.

Python

temperature = 23.5

This stores a True/False value in is_raining.

Python

is_raining = False

Sample Program

This program saves a name and age, then prints them out.

Python

name = "Bob"
age = 25
print(f"Name: {name}")
print(f"Age: {age}")

Important Notes

You can change a variable's value anytime by assigning a new value.

Variable names are case sensitive: Age and age are different.

Use meaningful names to make your code easier to understand.

Summary

Variable assignment stores values to use later.

Use = to assign values to variables.

Choose clear names and remember variables can change.

Practice

1. What does the following Python statement do?
age = 25

easy

A. Prints the value 25

B. Checks if age is equal to 25

C. Stores the value 25 in the variable named age

D. Deletes the variable age

Solution

1. Step 1: Understand the assignment operator

   The = sign in Python assigns the value on the right to the variable on the left.

2. Step 2: Analyze the statement age = 25

   This means the number 25 is stored inside the variable named age.

3. Final Answer:

   Stores the value 25 in the variable named age -> Option C

4. Quick Check:

   Assignment means storing value [OK]

Hint: Remember: '=' means store value, not compare [OK]

Common Mistakes:

• Confusing '=' with '==' for comparison
• Thinking '=' prints or deletes variables
• Assuming variable names are values

2. Which of the following is the correct way to assign the value 10 to a variable named count in Python?

easy

A. count == 10

B. count := 10

C. 10 = count

D. count = 10

Solution

1. Step 1: Identify the assignment operator

   In Python, the single equals sign = is used to assign values to variables.

2. Step 2: Check each option

   count == 10 uses == which is a comparison, not assignment. 10 = count tries to assign to a value, which is invalid. count := 10 uses walrus operator := which is valid in Python 3.8+, but not standard for simple assignment. count = 10 correctly assigns 10 to count.

3. Final Answer:

   count = 10 -> Option D

4. Quick Check:

   Use '=' for assignment [OK]

Hint: Use single '=' to assign values, not '==' [OK]

Common Mistakes:

• Using '==' instead of '=' for assignment
• Trying to assign value to a number
• Confusing walrus operator with assignment

3. What will be the output of this code?

name = "Alice"
age = 30
name = "Bob"
print(name, age)

medium

A. Alice 30

B. Bob 30

C. Alice 0

D. Bob 0

Solution

1. Step 1: Trace variable assignments

   Initially, name is set to "Alice" and age to 30. Then name is reassigned to "Bob".

2. Step 2: Understand print output

   The print statement outputs the current values of name and age. Since name was changed to "Bob", and age remains 30, the output is "Bob 30".

3. Final Answer:

   Bob 30 -> Option B

4. Quick Check:

   Last assignment wins [OK]

Hint: Last value assigned to variable is what prints [OK]

Common Mistakes:

• Thinking first assignment stays unchanged
• Confusing variable names or values
• Assuming age changes without assignment

4. Identify the error in this code snippet:

5number = 10
print(5number)

medium

A. Variable names cannot start with a number

B. Missing quotes around 5number

C. Assignment operator is wrong

D. print statement syntax error

Solution

1. Step 1: Check variable naming rules

   In Python, variable names must start with a letter or underscore, not a number.

2. Step 2: Analyze the code

   The variable name 5number starts with a digit, which is invalid syntax and causes an error.

3. Final Answer:

   Variable names cannot start with a number -> Option A

4. Quick Check:

   Variable names start with letter or underscore [OK]

Hint: Variable names cannot begin with digits [OK]

Common Mistakes:

• Starting variable names with numbers
• Confusing strings with variable names
• Assuming print syntax is wrong

5. You want to swap the values of two variables a and b in Python. Which of the following is the correct way to do it?

hard

A. a, b = b, a

B. a = b
b = a

C. temp = a
b = temp
a = b

D. a = a + b
b = a - b
a = a - b

Solution

1. Step 1: Understand swapping variables

   Swapping means exchanging values so that a gets b's value and b gets a's value.

2. Step 2: Analyze each option

   a = b b = a assigns b to a, then a to b, losing original a. temp = a b = temp a = b incorrectly assigns b before a. a = a + b b = a - b a = a - b uses arithmetic swap which works but is less clear and can cause errors with non-numbers. a, b = b, a uses Python's tuple unpacking to swap values correctly and clearly.

3. Final Answer:

   a, b = b, a -> Option A

4. Quick Check:

   Use tuple unpacking for swap [OK]

Hint: Swap with a, b = b, a for clean code [OK]

Common Mistakes:

• Overwriting variables before swapping
• Using temporary variable incorrectly
• Using arithmetic swap with non-numbers