What categories of data can be changed after their definition?

In Python, mutable data types are:

• Lists — elements can be changed, added, or removed.
• Dictionaries — key-value pairs can be modified.
• Sets — elements can be added or removed.

Immutable types include:

• Numbers (int, float, complex)
• Strings
• Tuples

Example of a mutable list:

my_list = [1, 2, 3]
my_list.append(4)  # Now my_list = [1, 2, 3, 4]

Example of an immutable string:

my_str = "hello"
# my_str[0] = 'H'  # Error, strings cannot be changed directly