There is a special case in
traceback.format_exception_only() for SyntaxError so
that the location of the syntax error is printed.
Unfortunately, the test is written so that it only
works with SyntaxError, but not for children of
SyntaxError, e.g. IndentationError.

OTOH, the interpreter prints the correct output if the
exception is allowed to terminate the program.

I have attached a test case that shows the difference
in output. With the current traceback.py module, the
output is different:

joe@pat py $ ./testSyntaxError.py
Traceback (most recent call last):
  File "./testSyntaxError.py", line 7, in ?
    import SyntaxErr
IndentationError: expected an indented block
(SyntaxErr.py, line 2)

joe@pat py $ ./testSyntaxError.py raise
Traceback (most recent call last):
  File "./testSyntaxError.py", line 7, in ?
    import SyntaxErr
  File "/home/joe/tmp/py/SyntaxErr.py", line 2
    class OtherClass:
        ^
IndentationError: expected an indented block

There's a second file that is needed for the test case,
I'll attach it as well.

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This file generates the IndentationError.

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This patch makes both the output of the interpreter and the
output generated by format_exception_only() identical.

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Fixed in rev. 43486. Thanks!