167 – Private members

Python has a very well-known naming convention: names that start with a leading underscore _ are considered “private”.

This means the outside world has no business using them. For example, attributes and methods starting with _ in a class mean they’re for that class only. When that happens, it’s common to see other methods of the class use those private names, like is the case for drive/_start_engine in the class Car:

class Car:
    def __init__(self, ...):
        self._serial_number = ...

    def _start_engine(self): ...

    def drive(self):
        self._start_engine()
        ...

Sometimes, private attributes/methods are still used inside the same module:

def _validate_serial_number(serial_no):
    ...

def inspect_car(workshop, car):
    if not _validate_serial_number(car._serial_number):
        ...

But if you’re importing someone else’s code, you should be very careful about using objects whose name starts with an underscore _.