Assignment and augmented assignment in Python - Step-by-Step Execution

Concept Flow - Assignment and augmented assignment

Start

↓

Assign value to variable

↓

Use variable in expression?

No→End

Yes↓

Perform calculation

↓

Update variable with new value

↓

Repeat or End

This flow shows how a variable gets a value, then can be updated using normal or augmented assignment.

Execution Sample

Python

x = 5
x += 3
x = x * 2
print(x)

Assign 5 to x, add 3 using +=, then multiply by 2, and print the result.

Execution Table

Step	Code executed	Variable x value	Explanation
1	x = 5	5	Assign 5 to x
2	x += 3	8	Add 3 to current x (5 + 3) and store back in x
3	x = x * 2	16	Multiply current x (8) by 2 and assign to x
4	print(x)	16	Output the current value of x
5	End	16	No more code to execute

💡 Program ends after printing x with value 16

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
x	undefined	5	8	16	16

Key Moments - 2 Insights

Why does x change from 5 to 8 after 'x += 3'?

Because 'x += 3' means 'add 3 to the current value of x and store it back in x', as shown in step 2 of the execution_table.

Is 'x = x * 2' the same as 'x *= 2'?

Yes, both multiply x by 2 and assign the result back to x. Step 3 shows the explicit form.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of x after step 2?

A 5

B 8

C 3

D 16

💡 Hint

Check the 'Variable x value' column at step 2 in the execution_table.

At which step does x get multiplied by 2?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Code executed' column for multiplication in the execution_table.

If we replace 'x += 3' with 'x = 3', what would be x after step 2?

A 8

B 5

C 3

D 16

💡 Hint

Replacing 'x += 3' with 'x = 3' sets x directly to 3, overriding previous value.

Concept Snapshot

Assignment sets a variable: x = 5
Augmented assignment updates it: x += 3 (means x = x + 3)
You can also use other operators: -=, *=, /=
They combine calculation and assignment in one step
Use augmented assignment for shorter, clearer code

Full Transcript

This example shows how assignment and augmented assignment work in Python. First, x is assigned the value 5. Then, using augmented assignment 'x += 3', we add 3 to x's current value, making it 8. Next, we multiply x by 2 with 'x = x * 2', updating x to 16. Finally, we print x, which outputs 16. Augmented assignment combines calculation and assignment in one step, making code shorter and easier to read.

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