Explain the purpose and principle of the __slots__ attribute in Python.

The __slots__ attribute in Python is used to restrict the set of attributes that instances of a class can have. This allows:

• Saving memory, as a __dict__ dictionary is not created for each object.
• Slightly speeding up attribute access.

How it works:

When you declare __slots__ in a class, you specify a fixed set of attribute names. Python creates a special internal storage for them instead of a regular dictionary.

Example:

class Point:
    __slots__ = ('x', 'y')

    def __init__(self, x, y):
        self.x = x
        self.y = y

p = Point(1, 2)
print(p.x, p.y)  # 1 2

# p.z = 3  # Error: cannot add attribute not specified in __slots__

Restrictions:

• Cannot dynamically add new attributes not specified in __slots__.
• Not suitable if a flexible set of attributes is needed.
• Not compatible with some inheritance mechanisms unless __slots__ is considered in subclasses.

Used for optimization in cases where many objects with a fixed set of attributes are created.