Assignment and augmented assignment in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the assignment operator = in Python?

The assignment operator = is used to store a value in a variable. It assigns the value on the right to the variable on the left.

beginner

What does the augmented assignment operator += do?

The += operator adds the value on the right to the variable on the left and then updates the variable with the new value. For example, x += 3 means x = x + 3.

beginner

List three common augmented assignment operators in Python.

Three common augmented assignment operators are:
1. += (add and assign)
2. -= (subtract and assign)
3. *= (multiply and assign)

beginner

What happens if you use x *= 2 when x is 5?

The value of x becomes 10 because x *= 2 means x = x * 2. So, 5 multiplied by 2 equals 10.

beginner

Can augmented assignment operators be used with strings? Give an example.

Yes, augmented assignment operators like += can be used with strings to concatenate them. For example:
text = 'Hello'
text += ' World'
Now, text is 'Hello World'.

What does the statement count -= 1 do?

A Subtracts 1 from count

B Divides count by 1

C Multiplies count by 1

D Adds 1 to count

The operator -= subtracts the value on the right (1) from the variable on the left (count).

Which of the following is equivalent to x += 5?

A x = 5 + x

B x = x - 5

C x = 5 - x

D x = x + 5

x += 5 means add 5 to x and assign the result back to x, which is x = x + 5.

What will be the value of text after this code?
text = 'Hi'
text += ' there'

A 'Hi there'

B 'Hi+ there'

C 'Hi'

D 'there'

The += operator concatenates the string ' there' to 'Hi', resulting in 'Hi there'.

If num = 10, what does num *= 3 do?

A Sets num to 13

B Sets num to 30

C Sets num to 7

D Sets num to 3

num *= 3 multiplies num by 3 and assigns the result back to num, so num becomes 30.

Which operator would you use to divide a variable by 4 and update it with the result?

A +=

B *=

C /=

D -=

The /= operator divides the variable by the value on the right and updates it.

Explain how assignment and augmented assignment operators work in Python with examples.

Think about how you store and update values in a variable.

Describe three different augmented assignment operators and what they do.

Focus on the operation and assignment combined.

Practice

1.

What does the += operator do in Python?

easy

A. Adds the right value to the left variable and updates it

B. Assigns a new variable without changing the old one

C. Subtracts the right value from the left variable

D. Creates a new list from two variables

Solution

1. Step 1: Understand the meaning of +=

   The += operator adds the value on the right to the variable on the left.

2. Step 2: Recognize it updates the variable

   It changes the original variable by adding the new value to it.

3. Final Answer:

   Adds the right value to the left variable and updates it -> Option A

4. Quick Check:

   += means add and assign [OK]

Hint: Think: add then store back in same variable [OK]

Common Mistakes:

• Confusing += with simple assignment =
• Thinking += creates a new variable
• Mixing += with subtraction or multiplication

2.

Which of the following is the correct syntax to add 5 to variable x using augmented assignment?

x = 10
# Add 5 to x here

easy

A. x =+ 5

B. x += 5

C. x =+5

D. x = x +

Solution

1. Step 1: Identify correct augmented assignment syntax

   The correct syntax to add and assign is x += 5.

2. Step 2: Check other options for syntax errors

   Choices like x =+ 5 and x =+5 use incorrect operator placement; x = x + is incomplete.

3. Final Answer:

   x += 5 -> Option B

4. Quick Check:

   Use += for adding and assigning [OK]

Hint: Remember: operator before equals for augmented assignment [OK]

Common Mistakes:

• Writing =+ instead of +=
• Leaving out the value after +
• Using incomplete expressions

3.

What is the output of this code?

count = 3
count += 4
count -= 2
print(count)

medium

A. 9

B. 7

C. 3

D. 5

Solution

1. Step 1: Calculate count += 4

   Starting from 3, adding 4 gives 7.

2. Step 2: Calculate count -= 2

   Subtracting 2 from 7 gives 5.

3. Final Answer:

   5 -> Option D

4. Quick Check:

   3 + 4 - 2 = 5 [OK]

Hint: Follow each operation step-by-step [OK]

Common Mistakes:

• Adding and subtracting in wrong order
• Confusing += and -= effects
• Ignoring the initial value

4.

Find the error in this code snippet:

total = 10
total + = 5
print(total)

medium

A. TypeError because + cannot be used with int

B. NameError because total is not defined

C. SyntaxError due to space in augmented assignment

D. No error, prints 15

Solution

1. Step 1: Check augmented assignment syntax

   The operator += must not have spaces between + and =.

2. Step 2: Identify the error caused by space

   Writing + = causes a SyntaxError in Python.

3. Final Answer:

   SyntaxError due to space in augmented assignment -> Option C

4. Quick Check:

   No spaces allowed in += operator [OK]

Hint: No spaces between + and = in augmented assignment [OK]

Common Mistakes:

• Adding spaces inside augmented assignment operator
• Assuming it works like normal addition
• Ignoring syntax error messages

5.

You have a variable score = 50. You want to increase it by 10%, then subtract 5 using augmented assignments. Which code correctly does this?

score = 50
# Increase by 10%
# Subtract 5

hard

A. score *= 1.1
score -= 5

B. score += 10
score -= 5

C. score = score + 10%
score = score - 5

D. score += 0.1
score -= 5

Solution

1. Step 1: Increase score by 10%

   Multiplying by 1.1 increases the value by 10%, so score *= 1.1 is correct.

2. Step 2: Subtract 5 using augmented assignment

   Use score -= 5 to subtract 5 from the updated score.

3. Final Answer:

   score *= 1.1 score -= 5 -> Option A

4. Quick Check:

   Multiply by 1.1 then subtract 5 [OK]

Hint: Use *= for percent increase, then -= for subtraction [OK]

Common Mistakes:

• Adding 10 instead of 10%
• Using invalid syntax like 10%
• Not updating score before subtracting