PEP 553 interactivity between `IPython.core.debugger.set_trace` and `python -m doctest` causes test failures

The promises of PEP 553 are pretty cool and even mention IPython by name. This and this seem to suggest that IPython.terminal.debugger.set_trace would be a good value for PYTHONBREAKPOINT. Indeed it does work:

File:

# test_case.py
def test_foo():
  one = "1"
  breakpoint()
  assert int(one) == 1

if __name__ == "__main__":
  test_foo()

Run:

% PYTHONBREAKPOINT='IPython.core.debugger.set_trace' python test_case.py
> /Users/matt/Documents/dev/dycelib/test_case.py(5)test_foo()
      3   one = "1"
      4   breakpoint()
----> 5   assert int(one) == 1
      6
      7 if __name__ == "__main__":

ipdb> dir()
['one']
ipdb> one
'1'
ipdb> c

However, breakpoints in doctests don’t work with IPython.core.debugger.set_trace. Consider:

# test_case.txt
>>> one = "1"
>>> breakpoint()
>>> int(one) == 1
True

This works:

% python -m doctest test_case.txt ; echo "exit code: ${?}"
--Return--
> <doctest test_case.txt[1]>(1)<module>()->None
-> breakpoint()
(Pdb) dir()
['__builtins__', '__name__', '__return__', 'one']
(Pdb) one
'1'
(Pdb) c
exit code: 0

Neat! Now try this:

% PYTHONBREAKPOINT='IPython.core.debugger.set_trace' python -m doctest test_case.txt ; echo "exit code: ${?}"
dir()
one
c
**********************************************************************
File "test_case.txt", line 3, in test_case.txt
Failed example:
    breakpoint()
Expected nothing
Got:
    --Return--
    None
    > <doctest test_case.txt[1]>(1)<module>()
    ----> 1 breakpoint()

    ipdb> ['__builtins__', '__name__', '__return__', 'one']
    ipdb> '1'
    ipdb>
**********************************************************************
1 items had failures:
   1 of   3 in test_case.txt
***Test Failed*** 1 failures.
exit code 1

Note that there is no interactivity or output until the end of the run (after typing c<RETURN>). Also, for some reason, IPython’s output is being considered by the test itself, so the test fails.

[MrMino]

Right. I edited my previous response to reflect that.

[posita]

Yup. Looks like prompt-toolkit is messing with doctest somehow: PYTHONBREAKPOINT=ipdb.sset_trace works properly.

It does sort of. EDIT: Removed as redundant.