type() and isinstance() in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the type() function do in Python?

The type() function returns the exact type of an object, such as int, str, or list.

beginner

What is the purpose of isinstance() in Python?

<p><code>isinstance()</code> checks if an object is an instance of a class or a subclass, returning <code>True</code> or <code>False</code>.</p>

intermediate

How is type() different from isinstance()?

<p><code>type()</code> checks for the exact type of an object, while <code>isinstance()</code> checks if the object is of a type or any subclass of that type.</p>

intermediate

What will isinstance(5, (int, float)) return and why?

It returns True because 5 is an int, and isinstance() can check against a tuple of types.

intermediate

Can <code>type()</code> be used to check if an object is a subclass instance?

<p>No, <code>type()</code> only checks the exact type, so it does not consider subclass relationships. Use <code>isinstance()</code> for that.</p>

What does type('hello') return?

A hello

B <class 'str'>

C string

D TypeError

type() returns the type of the object, which is str for a string.

Which function checks if an object is an instance of a class or its subclass?

A type()

B instance()

C class()

D isinstance()

isinstance() checks for instance and subclass relationships.

What will type(3.14) == float return?

A False

B 3.14

C True

D TypeError

type() returns the exact type, so this comparison is True.

Which is the correct way to check if obj is either an int or float?

A isinstance(obj, (int, float))

B type(obj) == int or float

C type(obj) in (int, float)

D isinstance(obj, int) and isinstance(obj, float)

isinstance() accepts a tuple of types to check against multiple types.

If class Dog(Animal): pass, what will type(dog) == Animal return if dog is a Dog instance?

A False

B True

C TypeError

D Depends on Python version

type() checks exact type, so it returns False because dog is a Dog, not Animal.

Explain the difference between type() and isinstance() in Python.

Think about how each function treats subclasses.

How can you check if a variable is either an integer or a float using Python built-in functions?

Remember isinstance() can check multiple types at once.

Practice

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

easy

A. It creates a new type.

B. It checks if an object is an instance of a class or its subclass.

C. It converts an object to a string.

D. It returns the exact type of an object.

Solution

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

   The type() function returns the exact type of the given object, like int, str, or list.

2. Step 2: Compare with other options

   isinstance() checks type inheritance, not exact type. Conversion or creation of types is not done by type().

3. Final Answer:

   It returns the exact type of an object. -> Option D

4. Quick Check:

   type(obj) = exact type [OK]

Hint: Remember: type() gives exact type, isinstance() checks inheritance [OK]

Common Mistakes:

• Confusing type() with isinstance()
• Thinking type() converts or creates types
• Assuming type() checks subclass relationships

2. Which of the following is the correct syntax to check if variable x is an instance of int?

easy

A. type(x) == isinstance(int)

B. isinstance(int, x)

C. isinstance(x, int)

D. type(x) is int()

Solution

1. Step 1: Recall the syntax of isinstance()

   The correct syntax is isinstance(object, class_or_tuple). So, isinstance(x, int) checks if x is an int or subclass.

2. Step 2: Analyze other options

   type(x) == isinstance(int) mixes type() and isinstance() wrongly. isinstance(int, x) reverses arguments. type(x) is int() incorrectly calls int as a function.

3. Final Answer:

   isinstance(x, int) -> Option C

4. Quick Check:

   isinstance(x, int) correct syntax [OK]

Hint: Use isinstance(obj, Type) to check type safely [OK]

Common Mistakes:

• Swapping arguments in isinstance()
• Using type() with wrong comparison
• Calling type names as functions in checks

3. What will be the output of this code?

class Animal:
    pass

class Dog(Animal):
    pass

x = Dog()
print(isinstance(x, Animal))
print(type(x) == Animal)

medium

A. True\nFalse

B. False\nTrue

C. True\nTrue

D. False\nFalse

Solution

1. Step 1: Understand isinstance() with inheritance

   x is an instance of Dog, which is a subclass of Animal. So, isinstance(x, Animal) returns True.

2. Step 2: Understand type() equality check

   type(x) returns Dog, which is not equal to Animal. So, type(x) == Animal returns False.

3. Final Answer:

   True\nFalse -> Option A

4. Quick Check:

   isinstance() checks inheritance, type() exact type [OK]

Hint: isinstance() True if subclass; type() True only if exact type [OK]

Common Mistakes:

• Assuming type() checks inheritance
• Confusing output order
• Thinking isinstance() returns False for subclass

4. Find the error in this code snippet:

def check_number(n):
    if type(n, int):
        return True
    else:
        return False

print(check_number(5))

medium

A. type() is used with two arguments incorrectly.

B. The function should use isinstance() instead of type().

C. The return statements are missing parentheses.

D. The print statement syntax is wrong.

Solution

1. Step 1: Check type() usage

   type() takes one argument to return the type. Using two arguments like type(n, int) is invalid and causes a TypeError.

2. Step 2: Identify correct usage

   To check if n is an int, use isinstance(n, int). The return statements and print syntax are correct.

3. Final Answer:

   type() is used with two arguments incorrectly. -> Option A

4. Quick Check:

   type() needs one argument [OK]

Hint: type() takes one argument; use isinstance() to check type [OK]

Common Mistakes:

• Passing two arguments to type()
• Confusing type() and isinstance() syntax
• Thinking return needs parentheses

5. You have a list of mixed data:

class MyInt(int):
    pass
items = [123, 'hello', 45.6, True, MyInt(456)]

. You want to create a new list containing only integers (including booleans, since they are subclasses of int). Which code correctly uses isinstance() to do this?

hard

A. ints = [x for x in items if type(x) is int or type(x) is bool]

B. ints = [x for x in items if isinstance(x, int)]

C. ints = [x for x in items if isinstance(x, bool)]

D. ints = [x for x in items if type(x) == int]

Solution

1. Step 1: Understand subclass behavior with isinstance()

   Booleans are subclasses of int in Python, so isinstance(True, int) returns True. Using isinstance(x, int) includes both ints and bools.

2. Step 2: Compare with other options

   ints = [x for x in items if type(x) == int] excludes bools because type(True) is bool, not int. ints = [x for x in items if isinstance(x, bool)] selects only bools, not ints. ints = [x for x in items if type(x) is int or type(x) is bool] is verbose and misses subclass flexibility.

3. Final Answer:

   ints = [x for x in items if isinstance(x, int)] -> Option B

4. Quick Check:

   isinstance() includes subclasses [OK]

Hint: Use isinstance(x, int) to include bools as ints [OK]

Common Mistakes:

• Using type() == int excludes bools
• Selecting only bools instead of ints
• Using complex or incorrect type checks