The function of double underscore back and front in a class function name?

[snippsat]

I read that a class is basically a dictionary. I believe the value of a dictionary key:value pair can be a function.

So in the case of class Car() do we have:

Car = {"color": 'blue', "mileage": 5, "fuel_efficiency": 14.5, "efficiency": calculate_gas_usage() }

Now is classes💪 is lot more that just a dictionary,it store values values from __init__ internally.
Can look at this:

>>> my_car = Car('blue', 8.8, 10.5)
>>> my_car.__dict__
{'color': 'blue', 'fuel_efficiency': 10.5, 'mileage': 8.8}
>>> my_car.__dict__['color']
'blue'

The calculate_gas_usage method is not stored in this dictionary.
Instead, it's a part of the class definition and is accessed through the class's namespace.
When you call my_car.calculate_gas_usage(distance),
Python automatically passes my_car as the first argument to the calculate_gas_usage method.

>>> my_car.calculate_gas_usage(275.5)
26.238095238095237