class A(object):
    def do_nothing(self):
        return self

    def fail(self, t):
        raise RuntimeError('fail')


def main():
    a = A()

    (a
        .do_nothing()
        .do_nothing()
        .fail(True)
        .fail(True)
        .do_nothing()
    )


if __name__ == '__main__':
    main()


# $ python3.7 script.py
# Traceback (most recent call last):
#   File "script.py", line 22, in <module>
#     main()
#   File "script.py", line 15, in main
#     .fail(True)
#   File "script.py", line 6, in fail
#     raise RuntimeError('fail')
# RuntimeError: fail

# $ python3.9 script.py
# Traceback (most recent call last):
#   File "/home/komendart/temp/script.py", line 22, in <module>
#     main()
#   File "/home/komendart/temp/script.py", line 12, in main
#     (a
#   File "/home/komendart/temp/script.py", line 6, in fail
#     raise RuntimeError('fail')
# RuntimeError: fail