What is meant by 'immutable types' and why are they called that?

Immutable types are data types whose values cannot be changed after creation. If you try to modify such a value, a new copy with the modified data is created, and the original remains unchanged.

In Python, examples of immutable types include:

• int
• float
• str
• tuple
• frozenset

Why are they called so:

• Once an object is created, its state cannot be changed.
• This ensures data safety and predictable behavior of programs.
• It simplifies working with multithreading, as immutable objects do not require synchronization.

For example, a string in Python is immutable:

s = "hello"
s2 = s.replace('h', 'j')  # A new string is created
print(s)  # hello
print(s2) # jello

Here, the replace method does not change the original string but returns a new one.