Python weirdie

results.txt

[seneca:~] $ ./tst.py
Making an A
Calling a.m1
In A.m1
In A._m2
In A._m3
Making an B
Calling b.m1
In A.m1
In A._m2
In B._m3

tst.py

#!/usr/bin/env python


class A:
    def m1(self):
        print('In A.m1')
        self._m2()

    def _m2(self):
        print('In A._m2')
        self._m3()

    def _m3(self):
        print('In A._m3')


class B(A):
    def _m3(self):
        print('In B._m3')


print('Making an A')
a = A()
print('Calling a.m1')
a.m1()

print('Making a B')
b = B()
print('Calling b.m1')
b.m1()