How to execute ipdb.set_trace() at will while running pytest tests

Question

I'm using pytest for my test suite. While catching bugs in complex inter-components test, I would like to place import ipdb; ipdb.set_trace() in the middle of my code to allow me to debug it.

However, since pytest traps sys.stdin/sys.stdout ipdb fails. How can I use ipdb while testing with pytest.

I'm not interested in jumping to pdb or ipdb after a failure, but to place breaks anywhere in the code and be able to debug it there before the failure occurs.

score 188 · Accepted Answer · edited Mar 16 '21 at 05:05

188

The error is raised because pytest captures output by default.

You can run pytest with -s option (turn off capture output). For example:

py.test -s my_test.py

and then in my_test.py:

import ipdb;
ipdb.set_trace()

edited Mar 16 '21 at 05:05

anon01

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answered May 06 '13 at 21:29

petRUShka

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In case one wants to do this in Django, add `addopts = -s` to `pytest.ini` file. – Rahul Gupta Dec 02 '15 at 17:18

score 68 · Answer 2 · edited Nov 04 '17 at 21:02

68

pytest-ipdb is unfortunately not supported anymore.

The solution is to run pytest my_test.py --pdb --pdbcls=IPython.terminal.debugger:Pdb

From the help command:

pytest -h
  --pdb                 start the interactive Python debugger on errors.
  --pdbcls=modulename:classname
                        start a custom interactive Python debugger on errors.
                        For example:
                        --pdbcls=IPython.terminal.debugger:TerminalPdb

The difference is just that TerminalPdb seems to throw erros, but Pdb not (Ipython docs).

edited Nov 04 '17 at 21:02

ivan_pozdeev

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answered Apr 12 '17 at 16:12

louis_guitton

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`TerminalPdb` is working again and the preferred solution as it will give you tab completion. – Uwe L. Korn Aug 05 '19 at 17:53
look out for ppdb, its got ipython quality introspection – msudder Apr 03 '20 at 16:20

score 7 · Answer 3 · answered Nov 27 '19 at 12:00

7

As of 2019-11 here is what should fix it:

pip install ipdb gnureadline ptpython

export PYTEST_ADDOPTS='--pdb --pdbcls=IPython.terminal.debugger:Pdb'

answered Nov 27 '19 at 12:00

sorin

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if you install `prompt-toolkit` version `2.0.10` then ipdb will work fine again, because it breaks due to recent update of this package to 3.0.0 – Pawel Barcik Nov 28 '19 at 09:56

score 3 · Answer 4 · answered Nov 15 '19 at 19:40

3

This is what I use

py.test tests/ --pdbcls=IPython.core.debugger:Pdb -s

answered Nov 15 '19 at 19:40

avoliva

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score 0 · Answer 5 · answered Sep 24 '21 at 19:40

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You may want to give pdbpp a try. I've had more success with it, compared to ipdb when used with pytest. See my answer here: https://stackoverflow.com/a/69320311/2896799.

answered Sep 24 '21 at 19:40

Apteryx

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How to execute ipdb.set_trace() at will while running pytest tests

5 Answers5