Immutable Types in Python

What you'll learn

Category	Types
Numbers	int, float, bool, complex
Text & bytes	str, bytes
Sequences	tuple, range
Special types	frozenset, NoneType

From the overview, you know immutable objects are replaced, not edited. This lesson walks through every built-in immutable type.

Visual hub of immutable types

Every type around the center cannot be modified in place.

Memory trick: If it is immutable, Python replaces the object instead of editing it.

1. Numeric types

Includes:

• int
• float
• bool
• complex

Key idea: Arithmetic creates a new object.

Visual proof

x = 10

print(id(x))

x = x + 5

print(x)
print(id(x))

Example output (your id() values will differ each run):

140245831990112
15
140245831991264

x = x + 5 does not modify 10; it creates a new integer object.

See: int · float · bool · complex

2. str and bytes

You can read characters by index, but you cannot replace them.

s = "python"

print(s[0])      # p

# s[0] = "P"     # TypeError

bytes behaves the same:

b = b"ABC"

# b[0] = 65      # TypeError

Rule: str and bytes are read-only sequences.

See: str · bytes · String Handling overview

3. tuple and range

Tuples look like lists — but they are fixed forever.

List vs tuple

t = (10, 20, 30)

print(t[1])      # 20

# t[0] = 99      # TypeError

Range:

r = range(5)

print(r[2])      # 2

# r[0] = 10      # TypeError

range generates values, but those values cannot be modified.

See: tuple · range

4. frozenset vs set

This is a favorite interview question.

Visual comparison

Type	Mutable?
set	Yes
frozenset	No

fs = frozenset([1, 2, 3])

# fs.add(4)      # AttributeError

s = {1, 2, 3}

s.add(4)         # Works

frozenset is simply a locked version of set.

See: frozenset · set

5. NoneType

None represents the absence of a value.

It is a singleton — only one None object exists in a program.

x = None
y = None

print(x is y)

Output:

True

Both variables reference the same object.

See: NoneType

Immutable checklist

If a type is immutable, these rules apply.

Test	Result
Item assignment	TypeError
In-place mutation	Not available
id() after modification	New object
Examples	str, tuple, int

Playground

Run this example and observe the behavior.

x = 10

print("int id before:", id(x))

x = x + 5

print("int id after:", id(x))

t = (1, 2, 3)

# t[0] = 9      # TypeError

fs = frozenset({1, 2, 3})

print(fs)

Observe:

• Integer → new ID
• Tuple → cannot modify
• Frozenset → fixed membership

Use the lesson playground at the bottom of the page to run this code live.

Quick knowledge check

1. Is tuple mutable?
   Answer: No — tuples are immutable.

2. Can you call add() on a frozenset?
   Answer: No — only a regular set supports add().

3. Does x = x + 1 modify the original integer?
   Answer: No — Python creates a new integer object.

30-second interview revision

Type	Remember
int, float	Arithmetic creates new objects
str, bytes	Read by index, cannot assign
tuple	Fixed sequence
range	Read-only generated values
frozenset	Immutable set
None	Singleton immutable object

Interview shortcut: If obj[index] = value raises TypeError, the object is immutable. If the object has methods like add() or append(), it is usually mutable.

Next: Mutable Types in Python.