Can you explain the concept of Python descriptors and provide examples of how they can be used to customize attribute access?

Descriptors allow customizing attribute access. Here's a simple example:

class Celsius:
    def __get__(self, instance, owner):
        return instance._celsius

    def __set__(self, instance, value):
        if value < -273.15:
            raise ValueError("Temperature below -273.15 is not possible.")
        instance._celsius = value

class Temperature:
    celsius = Celsius()

# Usage
temp = Temperature()
temp.celsius = 25
print(temp.celsius)