While learning thru advanced tutorials, it’s time to consolidate some basic concepts in Python. The explanation about property at https://www.programiz.com/python-programming/property is very clear. I’m writing an example below to remind myself of the private variable _cm being a convention only. Name like temp_cm works too.

Also cm is no longer a normal instance variable when property decorator is used. The design of adding @property allows backward compatible to keep codes unchanged!

class Unit:
    def __init__(self, cm=0):
        self.cm = cm

    def toInch(self):
        return self.cm * 0.3937

    # @property
    # def cm(self):
    #     return self.temp_cm
    # @cm.setter
    # def cm(self, v):
    #     self.temp_cm = v

unit = Unit(cm=100)

# {'cm': 100}        Without getter setter. The old way.
# {'temp_cm': 100}   With getter setter. The code still runs. It's backward compatible !