Dynamic typing in Python - Mini Project: Build & Apply

Dynamic typing in Python

📖 Scenario: Imagine you are creating a simple program that stores information about a product. The product's details can change, and you want to see how Python allows you to change the type of a variable easily.

🎯 Goal: You will create a variable to hold a product's price, then change its type from a number to a string, and finally to a boolean. This will show how Python's dynamic typing works.

📋 What You'll Learn

Create a variable called price and set it to the number 100

Create a variable called price and change its value to the string "One hundred"

Create a variable called price and change its value to the boolean True

Print the value and type of price after each change

💡 Why This Matters

🌍 Real World

Dynamic typing lets programmers write flexible code that can handle different kinds of data without strict type rules.

💼 Career

Understanding dynamic typing is important for Python developers to write clean and adaptable code in many real-world applications.

1

Create a variable with a number

Create a variable called price and set it to the number 100.

Python

# Create a variable called price and set it to 100
# Your code here

Hint

Use the equals sign = to assign the number 100 to the variable price.

2

Change the variable to a string

Change the variable price to the string "One hundred".

Python

price = 100
# Change price to the string "One hundred"
# Your code here

Hint

Assign the string "One hundred" to the variable price using =.

3

Change the variable to a boolean

Change the variable price to the boolean value True.

Python

price = 100
price = "One hundred"
# Change price to the boolean True
# Your code here

Hint

Assign the boolean value True to the variable price.

4

Print the value and type after each change

Print the value and type of price after each change using print(price, type(price)). You need to print three times: after setting it to 100, after changing to "One hundred", and after changing to True.

Python

price = 100
print(price, type(price))
price = "One hundred"
print(price, type(price))
price = True
print(price, type(price))
# Your code here

Hint

Use print(price, type(price)) after each assignment to show the value and its type.

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