Why doesn't Python (error msg) tell me WHAT the actual (arg) values are ?

[Peter J. Holzer]

On 2023-02-24 16:12:10 +1300, dn via Python-list wrote:
> In some ways, providing this information seems appropriate. Curiously, this
> does not even occur during an assert exception - despite the
> value/relationship being the whole point of using the command!
> 
>     x = 1
>     assert x == 2
> 
> AssertionError (and that's it)

Pytest is great there. If an assertion in a test case fails it analyzes
the expression to give you various levels of details:

======================================== test session starts ========================================
platform linux -- Python 3.10.6, pytest-6.2.5, py-1.10.0, pluggy-0.13.0
rootdir: /home/hjp/tmp/t
plugins: cov-3.0.0, anyio-3.6.1
collected 1 item

test_a.py F                                                                                   [100%]

============================================= FAILURES ==============================================
______________________________________________ test_a _______________________________________________

    def test_a():
        a = [1, 2, 3]
        b = {"a": a, "b": 2}

>       assert len(a) == len(b)
E       AssertionError: assert 3 == 2
E        +  where 3 = len([1, 2, 3])
E        +  and   2 = len({'a': [1, 2, 3], 'b': 2})

test_a.py:7: AssertionError
====================================== short test summary info ======================================
FAILED test_a.py::test_a - AssertionError: assert 3 == 2
========================================= 1 failed in 0.09s =========================================

        hp

-- 
   _  | Peter J. Holzer    | Story must make more sense than reality.
|_|_) |                    |
| |   | hjp at hjp.at         |    -- Charles Stross, "Creative writing
__/   | http://www.hjp.at/ |       challenge!"
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