[Python] How to run pytest with an python debugger with tab completion?

Background


I have been debugging my python scripts for ~2 years with plain from IPython import embed; embed(), and it has been working really fine. I just place the command on the line I want to examine, and when running the script I will have full IPython shell with capability for examining variables, defining functions, etc. On top of that, IPython shell comes with variable name tab completion.

Now, instead of always defining the "line of pause" with from IPython import embed; embed(), I would like my python scripts pause the execution while running tests, when they encounter an exception.

Question


How do you run pytest in such way, that

1. When an exception is raised, it launches python debugger
2. This debugger has tab completion for variable names?

Setup

• Windows 10
• Python 3.6

Simple failing test


# test_somemodule.py
def test_me(some_variable):
x = 1 + some_variable
return x


test_me('I am a string')


(No, you do not write tests for pytest like this, but for this exemplary purpose this is just fine.)

Solutions that do not work

1. pytest --pdb (with no pdbpp installed)


This opens the basic pdb shell when it runs to the error. But it has no tab completion.

-> x = 1 + some_variable
(Pdb) so[<tab_here_produces_tab>]

2. pytest --pdb (with pdbpp installed)


This opens the basic pdbpp shell when it runs to the error. But no tab completion.

-> x = 1 + some_variable
(Pdb++) so[<tab_here_produces_tab>]

3. pytest --pdb --pdbcls=IPython.terminal.debuggerdb


This opens the basic ipdb shell when it runs to the error. But no tab completion.

103
104 def test_me(some_variable):
--> 105 x = 1 + some_variable
106 return x
107

ipdb> so[<tab_here_produces_tab>]

4. fancycompleter.interact()


Tried fancycompleter.interact() as suggested here, no luck (with pdb, ipdb and pdbpp, fancycompleter v.0.8 and even this patched version.).

5. pytest --pdb -s


As Sergey Voronezhskiy commented, there is -s flag available for pytest. However, the tab completion works only partially: If there are multiple options for the same starting character(s), it will print out list of possible variables. This lacks the ability of quickly selecting one of the matching variables (which is available in IPython shell, for example):



Is there a way to make the variable name tab completion work? I would prefer ipdb or pdbpp over the vanilla pdb, but even a working solution with pdb is just fine.

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