What data types can serve as keys in Python dictionaries?

In Python, dictionary keys can only be immutable (hashable) data types. This means that the key must have a constant value and support the hash method.

Main key types:

• Numbers (int, float, complex)
• Strings (str)
• Tuples (tuple), if all elements inside are also hashable
• Boolean values (bool)

Mutable types such as lists (list), sets (set), dictionaries (dict) cannot be used because they are not hashable.

Example:

my_dict = {
    42: 'answer',
    'key': 'value',
    (1, 2): 'tuple key'
}