Exceptions without a traceback print multiple times if chained

[apple1417]

Minimal example:

def test_errors():
    ex1 = ValueError("abcd")
    ex2 = IndexError("efgh")
    ex3 = KeyError("ijkl")
    ex4 = RuntimeError("mnop")
    ex1.__cause__ = ex2
    ex2.__context__ = ex3
    ex3.__cause__ = ex4
    raise ex1

Which has the following output:

Expand

RuntimeError: mnop

The above exception was the direct cause of the following exception:
RuntimeError: mnop

The above exception was the direct cause of the following exception:

KeyError: 'ijkl'

During handling of the above exception, another exception occurred:
RuntimeError: mnop

The above exception was the direct cause of the following exception:

KeyError: 'ijkl'

During handling of the above exception, another exception occurred:

IndexError: efgh

The above exception was the direct cause of the following exception:

    def test_errors():
        ex1 = ValueError("abcd")
        ex2 = IndexError("efgh")
        ex3 = KeyError("ijkl")
        ex4 = RuntimeError("mnop")
        ex1.__cause__ = ex2
        ex2.__context__ = ex3
        ex3.__cause__ = ex4
>       raise ex1
E       ValueError: abcd

test.py:9: ValueError

What's happening is a little clearer when running with colourful output, the first, third and sixth "the above exception" lines are highlighted, but the rest are plain. Seems at each step of the chain, the full traceback for that exception is output, which includes that of any that happened higher in the chain. This only happens if __traceback__ is None, in practice I found this by messing with it on caught exceptions.

System details

Windows 10

> python --version
Python 3.9.0
> pip list
Package      Version
------------ -------
atomicwrites 1.4.0
attrs        20.3.0
colorama     0.4.4
iniconfig    1.1.1
packaging    20.9
pip          21.0.1
pluggy       0.13.1
py           1.10.0
pyparsing    2.4.7
pytest       6.2.2
setuptools   52.0.0
toml         0.10.2
wheel        0.36.2