Dynamic typing in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this dynamic typing example?

Consider the following Python code that uses dynamic typing. What will be printed?

Python

x = 5
x = 'hello'
print(x)

A TypeError

B 5

C NameError

D hello

💡 Hint

Remember, Python variables can change type at any time.

The variable x first holds an integer 5, then it is reassigned to a string 'hello'. The print statement outputs the current value, which is 'hello'.

❓ Predict Output

intermediate

What is the output when changing variable types?

What will this code print?

Python

a = 10
b = a
b = 'changed'
print(a)

A TypeError

B changed

C 10

D None

💡 Hint

Changing b does not affect a because integers are immutable.

Variable a remains 10 because b was assigned the value of a, not a reference that changes a.

❓ Predict Output

advanced

What error does this code raise?

What error will this code produce?

Python

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

A ValueError

B TypeError

C SyntaxError

D 5

💡 Hint

You cannot add an integer and a string directly.

Adding an integer and a string causes a TypeError in Python because they are incompatible types for addition.

❓ Predict Output

advanced

What is the output of this variable reassignment?

What will be printed by this code?

Python

var = [1, 2, 3]
var = 'now a string'
print(type(var))

A <class 'str'>

B <class 'list'>

C <class 'int'>

D TypeError

💡 Hint

The variable var is reassigned to a string.

The type of var after reassignment is str, so printing type(var) outputs .

🧠 Conceptual

expert

Which option best explains dynamic typing in Python?

Choose the statement that correctly describes dynamic typing in Python.

A Variables do not have types; only values have types, and variables can be reassigned to values of any type.

B Variables are statically typed and checked at compile time.

C Python requires explicit type declarations for all variables.

D Variables have fixed types and cannot change after assignment.

💡 Hint

Think about whether variables themselves have types or if types belong to values.

In Python, variables are just names that point to values. Values have types, and variables can be reassigned to values of any type at any time.

Practice

1. What does dynamic typing in Python mean?

easy

A. Python decides the variable type automatically when you assign a value.

B. You must declare the variable type before using it.

C. Variables cannot change their type once assigned.

D. Python uses only one data type for all variables.

Solution

1. Step 1: Understand dynamic typing concept

   Dynamic typing means Python figures out the type of a variable when you assign a value to it, without needing explicit declaration.

2. Step 2: Compare options with concept

   Python decides the variable type automatically when you assign a value. matches this idea. Requiring declaration before use and preventing type changes describe static typing, while claiming only one data type is incorrect because Python supports multiple types.

3. Final Answer:

   Python decides the variable type automatically when you assign a value. -> Option A

4. Quick Check:

   Dynamic typing = automatic type assignment [OK]

Hint: Dynamic typing means no need to declare types explicitly [OK]

Common Mistakes:

• Thinking variables need type declaration
• Believing variable types cannot change
• Confusing dynamic typing with static typing

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

easy

A. x = 5

B. x := 5

C. int x = 5

D. var x = 5

Solution

1. Step 1: Recall Python assignment syntax

   In Python, variables are assigned using the equals sign without type declaration or keywords.

2. Step 2: Check each option

   x = 5 uses correct syntax. int x = 5 is from languages like C/Java, := is the walrus operator but requires context, var x = 5 is from JavaScript.

3. Final Answer:

   x = 5 -> Option A

4. Quick Check:

   Assignment uses = without type [OK]

Hint: Use simple equals sign for assignment in Python [OK]

Common Mistakes:

• Using type declarations like int or var
• Confusing walrus operator with assignment
• Adding semicolons or extra symbols

3. What will be the output of this code?

var = 10
var = 'hello'
print(var)

medium

A. 10

B. hello

C. Error: cannot change variable type

D. None

Solution

1. Step 1: Follow variable assignments

   First, var is assigned the number 10, then it is reassigned the string 'hello'.

2. Step 2: Understand dynamic typing effect

   Python allows changing variable types, so print(var) outputs the last assigned value, hello.

3. Final Answer:

   hello -> Option B

4. Quick Check:

   Variable type changes allowed = hello output [OK]

Hint: Last assigned value is printed regardless of type change [OK]

Common Mistakes:

• Expecting error on type change
• Printing the first assigned value
• Confusing variable declaration rules

4. Find the error in this code snippet:

x = 5
x = 'five'
print(x + 2)

medium

A. No error, output is 'five2'

B. NameError because x is undefined

C. TypeError because you cannot add string and int

D. SyntaxError due to reassignment

Solution

1. Step 1: Analyze variable types and operation

   x is first an int (5), then a string ('five'). The print statement tries to add x + 2, which is string + int.

2. Step 2: Understand Python's type rules

   Python does not allow adding string and int directly, causing a TypeError.

3. Final Answer:

   TypeError because you cannot add string and int -> Option C

4. Quick Check:

   Adding string + int causes TypeError [OK]

Hint: Cannot add different types like string and int directly [OK]

Common Mistakes:

• Thinking Python auto-converts types in addition
• Expecting concatenation without conversion
• Ignoring type mismatch errors

5. You want to store a user's age and then later change it to a string message. Which code correctly uses dynamic typing to do this without error?

hard

A. age = 25
age = age + ' years old'
print(age)

B. age = '25'
age = age + 5
print(age)

C. age = 25
age = age + 5
age = ' years old'
print(age)

D. age = 25
age = str(age) + ' years old'
print(age)

Solution

1. Step 1: Check each option for type compatibility

   age = 25 age = age + ' years old' print(age) tries to add int and string directly, causing error. age = 25 age = str(age) + ' years old' print(age) converts int to string before concatenation, which is correct. age = '25' age = age + 5 print(age) tries to add int to string, error. age = 25 age = age + 5 age = ' years old' print(age) adds ints then replaces with string, but print shows string only.

2. Step 2: Identify correct dynamic typing usage

   age = 25 age = str(age) + ' years old' print(age) properly converts type before concatenation, avoiding errors and showing expected output.

3. Final Answer:

   age = 25 age = str(age) + ' years old' print(age) -> Option D

4. Quick Check:

   Convert int to string before concatenation [OK]

Hint: Convert types explicitly before mixing them in operations [OK]

Common Mistakes:

• Adding int and string without conversion
• Assuming Python auto-converts types in addition
• Overwriting variables without proper conversion