Problem mit Approx

[antonykamp]

Hey guy,

I have a little problem with the function approx. I use it alot in a project, but in one situation it looks like the code by this guy.

Here is the spesific file, the line of code at 853:
assert constr_value[0] == pytest.approx(0, 1e-5)

The error:

E           assert -1.758637679927233e-11 == 0 ± 1.0e-12
E            +  where 0 ± 1.0e-12 = <function approx at 0x000001BB36AF9400>(0, 1e-11)
E            +    where <function approx at 0x000001BB36AF9400> = pytest.approx

I'm using the pytest version 4.3.1 from Anaconda3 and win 10 and these are my packages.

[The-Compiler]

I don't follow. You expect a value to be 0 ± 1.0e-12 but it is -1.758637679927233e-11 which is far smaller (i.e. further away from 0).

[antonykamp]

I know and i don't want it. I expected a value 0 ± 1e-5 (see code line), but pytest ignores my decision and uses 1e-12

[kalekundert]

I think the problem is that you specified a relative tolerance instead of an absolute tolerance, and anything relative to 0 is still 0. Try this instead:

assert constr_value[0] == pytest.approx(0, abs=1e-5)

The logic behind all of this is explained here: https://docs.pytest.org/en/latest/reference.html#pytest-approx

[antonykamp]

Great! Now it works like expected. Thanks for your quick help. 👍