Explain the concept of slots in Python and what they are used for.

In Python, __slots__ is a mechanism that allows you to restrict the set of attributes that instances of a class can have, thereby saving memory.

By default, class instances store their attributes in a __dict__ dictionary, which consumes additional memory. If you define an attribute __slots__ in a class as a tuple of allowed attribute names, Python will not create a dictionary for each object but will allocate a fixed space for the specified attributes.

This is useful when creating a large number of objects and memory optimization is important.

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  # will raise AttributeError because 'z' is not in __slots__

Thus, __slots__ helps save memory and prevents the dynamic addition of new attributes.