Dynamic typing in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does dynamic typing mean in Python?

Dynamic typing means you don't have to declare variable types explicitly. Python figures out the type when you assign a value.

beginner

Can a Python variable change its type during the program?

Yes! A variable can hold a value of one type and later hold a value of a different type without errors.

beginner

Example: What is the type of 'x' after these lines?

x = 5
x = 'hello'

After the first line, x is an integer. After the second line, x becomes a string. Python changes the type automatically.

intermediate

Does dynamic typing mean Python is weakly typed?

No. Python is strongly typed because it keeps track of types and does not allow mixing incompatible types without explicit conversion.

beginner

Why is dynamic typing helpful for beginners?

It lets you write code faster without worrying about types. You can focus on solving problems instead of declaring types.

What happens when you assign a new value of a different type to a Python variable?

A The program crashes.

B Python throws a type error.

C The variable keeps the old type.

D The variable changes to the new type automatically.

Python variables can change types dynamically when assigned new values.

Which of these is true about Python's typing?

A Python is statically typed.

B Python requires explicit type declarations.

C Python is dynamically typed.

D Python variables cannot change type.

Python determines variable types at runtime, so it is dynamically typed.

Is Python strongly typed or weakly typed?

A Strongly typed

B Weakly typed

C Neither

D Both

Python is strongly typed because it enforces type rules and does not allow implicit mixing of incompatible types.

What is a benefit of dynamic typing for new programmers?

A They must declare all types before use.

B They can write code without worrying about types.

C They cannot change variable types.

D They must convert types manually all the time.

Dynamic typing lets beginners focus on logic without declaring types.

What type will variable 'a' have after these lines?

a = 10
a = 3.14

A float

B str

C int

D bool

After assigning 3.14, 'a' becomes a float type.

Explain what dynamic typing means in Python and how it affects variable usage.

Think about how Python handles variable types when you assign new values.

Describe the difference between dynamic typing and strong typing in Python.

Consider how Python decides types and how strictly it enforces type rules.

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