Variable assignment in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is variable assignment in Python?

Variable assignment means giving a name to a value so you can use it later. For example, x = 5 means the name x now holds the value 5.

beginner

How do you assign multiple variables in one line in Python?

You can assign multiple variables by separating them with commas. For example, a, b = 1, 2 assigns 1 to a and 2 to b.

beginner

What happens if you assign a new value to an existing variable?

The old value is replaced by the new one. For example, if x = 5 and then x = 10, x now holds 10.

beginner

Can variable names in Python start with a number?

No, variable names cannot start with a number. They must start with a letter (a-z, A-Z) or an underscore (_).

beginner

What is the difference between = and == in Python?

= is used to assign a value to a variable. == is used to check if two values are equal.

Which of the following is a valid variable assignment in Python?

A score = 100

B 100 = score

C score == 100

D score := 100

Option A correctly assigns 100 to the variable 'score'. Option B tries to assign to a number, which is invalid. Option C is a comparison, not assignment. Option D uses walrus operator which is valid in expressions but not for simple assignment statements.

What will be the value of 'a' after this code?
a = 5
a = 10

A 5

B 15

C 10

D Error

The second assignment replaces the first, so 'a' holds 10.

Which variable name is NOT valid in Python?

A value_2

B _value

C value2

D 2ndValue

Variable names cannot start with a number, so '2ndValue' is invalid.

How do you assign the values 1, 2, and 3 to variables x, y, and z in one line?

A x = y = z = 1, 2, 3

B x, y, z = 1, 2, 3

C x = 1; y = 2; z = 3

D x, y, z == 1, 2, 3

Option B correctly assigns 1 to x, 2 to y, and 3 to z in one line.

What does the '=' symbol do in Python?

A Assigns a value to a variable

B Checks if two values are equal

C Starts a comment

D Ends a statement

'=' assigns the value on the right to the variable on the left.

Explain how to assign a value to a variable in Python and what rules variable names must follow.

Think about how you give a name to a box and put something inside.

Describe what happens when you assign a new value to an existing variable.

Imagine replacing the content inside a labeled box.

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