Testing encapsulation in Python3

python_enc.py

#!/usr/bin/python3

class Phone:
    username = "Kate"                # public variable
    __serial_number = "11.22.33"     # private variable
    __how_many_times_turned_on = 0   # private variable

    def __init__(self):              # constructor
        print( "The Phone object was created" )
        self.__turn_on()

    def call(self):                  # public method
        print( "Ring-ring!" )

    def __turn_on(self):             # private method
        self.__how_many_times_turned_on += 1 
        print( "Times was turned on: ", self.__how_many_times_turned_on )

# initializing class object
my_phone = Phone()

print( "Testing public access to public data" )
# calling public method
my_phone.call()
# printing public variable
print( "The username is ", my_phone.username )

print( "Testing public access to private data" )
"""
Trying to run private method as public method won't work:
my_phone.turn_on()   - No
my_phone.__turn_on() - No again
However, gaining access through calling class will succeed
"""
# calling private method
my_phone._Phone__turn_on()
# printing private variable
print( "The serial number is ", my_phone._Phone__serial_number )
# modifying private variable
my_phone._Phone__serial_number = "44.55.66"
print( "New serial number is ", my_phone._Phone__serial_number )
input( "Press Enter to exit" )