Type checking using type() in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the type() function do in Python?

The type() function tells you the type of a value or variable, like whether it is a number, text, list, or something else.

beginner

How do you check if a variable x is an integer using type()?

You compare type(x) to int like this: type(x) == int. If it is true, x is an integer.

beginner

What will type('hello') return?

It will return <class 'str'> because 'hello' is a string (text).

beginner

Can type() be used to check the type of a list?

Yes, for example type([1, 2, 3]) == list will be True because the value is a list.

intermediate

Is type() useful for making decisions in code?

Yes, you can use type() in if statements to run different code depending on the type of a variable.

What does type(3.14) return?

A <class 'float'>

B <class 'int'>

C <class 'str'>

D <class 'bool'>

3.14 is a decimal number, so its type is float.

How do you check if variable y is a string?

A type(y) == bool

B type(y) == int

C type(y) == list

D type(y) == str

Strings have the type str, so you compare type(y) to str.

What will type(True) return?

A <class 'int'>

B <class 'bool'>

C <class 'str'>

D <class 'float'>

True is a boolean value, so its type is bool.

Which of these is NOT a valid use of type()?

A Changing the type of a variable

B Checking if a variable is a list

C Checking if a variable is an integer

D Finding the type of a string

type() only tells you the type; it does not change the type of a variable.

What does type([1, 2, 3]) == list evaluate to?

A False

B Error

C True

D None

The value is a list, so type([1, 2, 3]) is list, making the comparison true.

Explain how to use type() to check if a variable is a string or an integer.

Think about comparing the result of type() to the type name.

Describe a simple real-life example where checking the type of a variable with type() might be useful.

Imagine you get different kinds of data and want to treat them differently.

Practice

1. What does the type() function do in Python?

easy

A. It tells you the kind of data stored in a variable.

B. It changes the data type of a variable.

C. It prints the value of a variable.

D. It deletes a variable from memory.

Solution

1. Step 1: Understand the purpose of type()

   The type() function returns the data type of the given variable or value.

2. Step 2: Compare options with the function's purpose

   Only It tells you the kind of data stored in a variable. correctly states that type() tells the kind of data stored in a variable.

3. Final Answer:

   It tells you the kind of data stored in a variable. -> Option A

4. Quick Check:

   type() returns data type [OK]

Hint: Remember: type() shows data kind, not value or change [OK]

Common Mistakes:

• Thinking type() changes the variable's type
• Confusing type() with print()
• Assuming type() deletes variables

2. Which of the following is the correct syntax to check the type of variable x?

easy

A. type x

B. type[x]

C. type(x)

D. check_type(x)

Solution

1. Step 1: Recall the syntax of the type() function

   The correct syntax uses parentheses around the variable: type(x).

2. Step 2: Evaluate each option

   type(x) matches the correct syntax. Options A and B use wrong brackets or missing parentheses. check_type(x) is not a valid Python function.

3. Final Answer:

   type(x) -> Option C

4. Quick Check:

   Use parentheses with type() [OK]

Hint: Use parentheses with functions like type() [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Omitting parentheses
• Using non-existent functions like check_type()

3. What will be the output of this code?

value = 3.14
print(type(value))

medium

A. <class 'float'>

B. <class 'int'>

C. <class 'str'>

D. Error

Solution

1. Step 1: Identify the data type of value

   The variable value is assigned 3.14, which is a decimal number, so its type is float.

2. Step 2: Understand what print(type(value)) outputs

   The type() function returns <class 'float'> for a float value, which is printed.

3. Final Answer:

   <class 'float'> -> Option A

4. Quick Check:

   3.14 is float type [OK]

Hint: Decimals are float type in Python [OK]

Common Mistakes:

• Confusing float with int
• Expecting string output
• Thinking it causes an error

4. Find the error in this code snippet:

my_var = 'hello'
if type(my_var) == str:
print('It is a string')

medium

A. Missing colon after if statement

B. Indentation error in print statement

C. Variable name is invalid

D. Incorrect use of type() function

Solution

1. Step 1: Check the if statement syntax

   The if statement has a colon and uses type() correctly, so no error there.

2. Step 2: Check indentation of the print statement

   In Python, the code inside if must be indented. Here, print is not indented, causing an indentation error.

3. Final Answer:

   Indentation error in print statement -> Option B

4. Quick Check:

   Indent inside if blocks [OK]

Hint: Indent code inside if statements [OK]

Common Mistakes:

• Forgetting to indent after if
• Misusing type() comparison
• Missing colon after if

5. You want to write a function that returns True if the input is an integer or a float, and False otherwise. Which code correctly uses type() to do this?

hard

A. def check_num(x):
return type(x) == int and float

B. def check_num(x):
return type(x) == int or float

C. def check_num(x):
return type(x) == 'int' or 'float'

D. def check_num(x):
return type(x) in [int, float]

Solution

1. Step 1: Understand the goal

   The function should return True if x is either int or float.

2. Step 2: Analyze each option's correctness

   def check_num(x): return type(x) == int or float uses or float incorrectly, always returning truthy. def check_num(x): return type(x) in [int, float] uses in to check membership in a list of types, which is concise and correct. def check_num(x): return type(x) == 'int' or 'float' compares type to strings, which is wrong. def check_num(x): return type(x) == int and float uses and incorrectly, only detecting ints.

3. Final Answer:

   def check_num(x): return type(x) in [int, float] -> Option D

4. Quick Check:

   Use in to check multiple types [OK]

Hint: Use 'type(x) in [int, float]' for multiple types [OK]

Common Mistakes:

• Comparing type to string names
• Using 'and' instead of 'or' or 'in'
• Using incomplete logic like '== int or float'