Inconsistent line breaking and parenthesis with pow and floor-div

[Cielquan]

Describe the bug I have two lines which are same except for one line using ** and one line using // as operator. When I black the file both lines are broken differently. And for the ** unnecessary parenthesis are added on the mathematical expression on the right side of the assert statement. When I remove them manually afterwards and run black again, they are not added again.

To Reproduce Steps to reproduce the behavior:

1. Write this to a file:

   def test_this():
   if True:
       assert StrCalc.calculate_string("+{num_l}**+{num_r}".format(num_l=num_l, num_r=num_r)) == +num_l ** +num_r
       assert StrCalc.calculate_string("+{num_l}//+{num_r}".format(num_l=num_l, num_r=num_r)) == +num_l // +num_r

2. Run black on it with line-length set to 88
3. See bugs:

   def test_this():
   if True:
       assert StrCalc.calculate_string(
           "+{num_l}**+{num_r}".format(num_l=num_l, num_r=num_r)
       ) == +(num_l ** +num_r)
       assert (
           StrCalc.calculate_string(
               "+{num_l}//+{num_r}".format(num_l=num_l, num_r=num_r)
           )
           == +num_l // +num_r
       )

Expected behavior A clear and concise description of what you expected to happen. I expected both lines to be broken the same and the unnecessary parenthesis are not added.

Environment (please complete the following information):

• Version: 20.8b1
• OS and Python version: Win10/Python 3.8.2]

Does this bug also happen on master? I used the online formatter and yes.

[JelleZijlstra]

This presumably has something to do with the relative precedences of unary +, //, and ** (https://docs.python.org/3/reference/expressions.html#operator-precedence).

[JelleZijlstra]

Still formats the same on current main.