Python 3.5- compatibility issue about black HOT 8 CLOSED

Kenneth's right. The README states you should be able to reformat even well-behaved Python 2.7 code. This is simply an omission on my part because I don't run Python 2.7 on my own projects anymore.

But, the **kwargs trailing comma is such a small thing to fix that will unlock compatibility with 2.7-3.5 that I'm going to do it for sure.

from black.

I don't think this is an issue. The docs clearly state python3.6+ compatibility.

from black.

No, the tool is to be run on Python 3.6, but is to produce code compatible with even Python 2.

from black.

Watch out that this also affects

def foo(*args,):  # error on 3.5 and earlier
    ...

def foo(a, *, b,): # error on 3.5 and earlier
    ...

(For reference it's bpo-9232.)

from black.

Yes, I'm familiar with the additional forms. Essentially, whenever the argument list includes a star, it's no longer safe to use a trailing comma unless such trailing comma or an f-string was already present in the file (which signifies the code is already 3.6+).

from black.

from black.

Yes, that's the flip side. An easy way to spot those for you would be to run:

$ python3.5 -m compileall .

in your directory and see where you have failures. Hopefully there's not going to be too many. Let me know, if so I'll add a temporary option to never add trailing commas so you can fix your early adopter misformattings :-)

from black.

This is now fixed as described above. @kennethreitz, let me know if you need help with unbreaking the 3.6-only formattings in your code. If those are pushed to GitHub, I will happily make a pull request that undoes the damage.

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