How variable type changes at runtime in Python - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of variable type changes?

Consider the following Python code where a variable changes its type during execution. What will be printed?

Python

x = 10
print(type(x))
x = 'hello'
print(type(x))

A <class 'int'>\n<class 'str'>

B <class 'str'>\n<class 'int'>

C <class 'int'>\n<class 'int'>

D TypeError

💡 Hint

Remember that Python variables can hold values of any type and can change types anytime.

Initially, x is assigned an integer 10, so type(x) is int. Then x is assigned a string 'hello', so type(x) becomes str.

❓ Predict Output

intermediate

What is the final type of variable after reassignment?

Look at this code where a variable is reassigned multiple times. What is the type of variable 'data' at the end?

Python

data = 3.14
print(type(data))
data = [1, 2, 3]
print(type(data))
data = {'a': 1}
print(type(data))

A <class 'int'>\n<class 'list'>\n<class 'dict'>

B <class 'float'>\n<class 'dict'>\n<class 'list'>

C <class 'float'>\n<class 'list'>\n<class 'dict'>

D SyntaxError

💡 Hint

Check the type after each assignment carefully.

The variable 'data' first holds a float, then a list, then a dictionary. Each print shows the current type.

❓ Predict Output

advanced

What is the output when variable type changes inside a function?

What will this code print when a variable changes type inside a function?

Python

def change_var():
    var = 5
    print(type(var))
    var = 'changed'
    print(type(var))

change_var()

A <class 'str'>\n<class 'int'>

B <class 'int'>\n<class 'int'>

C NameError

D <class 'int'>\n<class 'str'>

💡 Hint

Variables inside functions behave the same way as outside in terms of type changes.

Inside the function, var starts as int, then changes to str. Both types print accordingly.

❓ Predict Output

advanced

What error occurs when using variable before assignment after type change?

What error will this code raise when a variable is used before assignment after changing its type?

Python

x = 10
print(x)
x = x + '5'
print(x)

A SyntaxError

B TypeError

C NameError

D No error, prints 15

💡 Hint

Think about what happens when you add an integer and a string.

Adding int and str causes a TypeError because Python cannot combine these types directly.

🧠 Conceptual

expert

How does Python handle variable types at runtime?

Which statement best describes how Python handles variable types during program execution?

A Python variables are dynamically typed and can change type when assigned new values.

B Python requires explicit type declarations before assigning values.

C Python variables have fixed types assigned at declaration and cannot change.

D Python variables are statically typed and checked at compile time.

💡 Hint

Think about how you can assign different types to the same variable name in Python.

Python is dynamically typed, meaning variables can hold any type and change type during execution.

Practice

1. What happens to the type of a Python variable when you assign a new value of a different type to it?

easy

A. The variable's type changes to the new value's type automatically.

B. The variable keeps its original type regardless of the new value.

C. Python raises an error if the new value's type is different.

D. The variable becomes a list containing both old and new types.

Solution

1. Step 1: Understand Python variable typing

   Python variables are dynamically typed, meaning their type depends on the current value assigned.

2. Step 2: Assigning a new value changes the type

   When you assign a new value of a different type, the variable's type updates to match the new value automatically.

3. Final Answer:

   The variable's type changes to the new value's type automatically. -> Option A

4. Quick Check:

   Python variables are dynamic = A [OK]

Hint: Remember: Python variables follow the value's type, not fixed type. [OK]

Common Mistakes:

• Thinking variables have fixed types like in some other languages.
• Assuming Python throws an error on type change.
• Believing variable types combine old and new types.

2. Which of the following is the correct way to assign a new value to a variable in Python so its type changes?

easy

A. x = 10

B. x := 10

C. int x = 10

D. var x = 10

Solution

1. Step 1: Identify Python assignment syntax

   Python uses the single equals sign (=) to assign values to variables.

2. Step 2: Check each option

   x = 10 uses correct syntax. x := 10 uses walrus operator which is for expressions, not simple assignment. int x = 10 and var x = 10 are invalid in Python.

3. Final Answer:

   x = 10 -> Option A

4. Quick Check:

   Assignment uses = in Python = A [OK]

Hint: Use single '=' for assignment in Python, not ':=' or types. [OK]

Common Mistakes:

• Confusing ':=' walrus operator with assignment.
• Using typed declarations like other languages.
• Trying to declare variable types explicitly.

3. What will be the output of this code?

var = 5
print(type(var))
var = 'hello'
print(type(var))

medium

A. \n

B. \n

C. \n

D. Error

Solution

1. Step 1: Check initial assignment and type

   var is first assigned 5, an integer, so type(var) is <class 'int'>.

2. Step 2: Reassign and check new type

   var is then assigned 'hello', a string, so type(var) is <class 'str'>.

3. Final Answer:

   <class 'int'>\n<class 'str'> -> Option C

4. Quick Check:

   Type changes with value = C [OK]

Hint: Track variable type after each assignment line by line. [OK]

Common Mistakes:

• Assuming type stays the same after reassignment.
• Confusing output order of print statements.
• Expecting a runtime error on type change.

4. Find the error in this code snippet:

value = 10
value = value + '5'
print(value)

medium

A. NameError because 'value' is undefined

B. SyntaxError due to invalid assignment

C. No error, output is 15

D. TypeError because int and str cannot be added

Solution

1. Step 1: Analyze the operation between int and str

   value is an int (10), then tries to add a string ('5'), which is not allowed.

2. Step 2: Identify the error type

   Python raises a TypeError when adding incompatible types like int and str.

3. Final Answer:

   TypeError because int and str cannot be added -> Option D

4. Quick Check:

   Adding int + str causes TypeError = D [OK]

Hint: Check types before adding; int + str causes error. [OK]

Common Mistakes:

• Thinking Python auto-converts types in addition.
• Expecting output '15' as string concatenation.
• Confusing SyntaxError with TypeError.

5. Given the code below, what will be the final type of data?

data = 100
if isinstance(data, int):
    data = str(data)
else:
    data = [data]

hard

A. int

B. str

C. list

D. bool

Solution

1. Step 1: Check initial type of data

   data starts as 100, which is an int.

2. Step 2: Evaluate the if condition

   Since data is int, the if block runs, converting data to str('100').

3. Final Answer:

   str -> Option B

4. Quick Check:

   int converted to str by condition = B [OK]

Hint: If int, convert to str; else make list. [OK]

Common Mistakes:

• Ignoring the if condition and assuming list.
• Thinking data remains int after reassignment.
• Confusing str and bool types.