type() and isinstance() in Python - Step-by-Step Execution

Concept Flow - type() and isinstance()

Start with a variable

↓

Use type() to get exact type

↓

Use isinstance() to check if variable is a type or subclass

↓

If True

→Do something

↓

If False

→Do something else

↓

End

First, get the variable's exact type with type(). Then, check if it matches or inherits a type using isinstance(). Based on that, decide what to do.

Execution Sample

Python

x = 5
print(type(x))
print(isinstance(x, int))
print(isinstance(x, str))

This code shows the type of x and checks if x is an int or a str.

Execution Table

Step	Action	Expression	Result	Explanation
1	Assign	x = 5	x = 5	Variable x is set to integer 5
2	Check type	type(x)	<class 'int'>	x is exactly of type int
3	Check isinstance	isinstance(x, int)	True	x is an instance of int or subclass
4	Check isinstance	isinstance(x, str)	False	x is not an instance of str or subclass

💡 All checks done, program ends

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
x	undefined	5	5	5	5

Key Moments - 2 Insights

Why does type(x) return <class 'int'> but isinstance(x, int) returns True?

type(x) shows the exact type of x (int). isinstance(x, int) returns True because x is an instance of int or any subclass of int. They are related but used differently as shown in execution_table rows 2 and 3.

Why does isinstance(x, str) return False even though x is a number?

Because x is not an instance of str or any subclass of str. isinstance checks if x belongs to the given type or its subclasses, as seen in execution_table row 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the result of type(x) at step 2?

A False

B True

C <class 'int'>

D 5

💡 Hint

Check the 'Result' column in execution_table row 2

At which step does isinstance(x, int) return True?

A Step 3

B Step 2

C Step 4

D Step 1

💡 Hint

Look at the 'Action' and 'Result' columns in execution_table row 3

If x was a string 'hello', what would isinstance(x, str) return at step 4?

A False

B True

C <class 'str'>

D Error

💡 Hint

Refer to how isinstance works in execution_table row 4 and key_moments explanation

Concept Snapshot

type(variable) returns the exact type of variable.
isinstance(variable, type) checks if variable is of that type or subclass.
Use type() to get type info.
Use isinstance() to check type safely.
isinstance() works with inheritance; type() does not.

Full Transcript

We start by assigning the value 5 to variable x. Then, we use type(x) to find out the exact type of x, which is int. Next, we check if x is an instance of int using isinstance(x, int), which returns True because x is indeed an integer. Finally, we check if x is an instance of str using isinstance(x, str), which returns False because x is not a string. This shows how type() gives the exact type, while isinstance() checks if the variable belongs to a type or its subclasses.

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