This is a collection of no-op statements that are syntactically valid only since Python X.Y, for most X.Y ≥ 2.4.
0_0 # Python >= 3.6 is required
The idea is to put such a statement near the top of your file. If a user inadvertently ran the code against an older version, they would get a fairly helpful error message:
$ python3.5 since-3.6.py File "since-3.6.py", line 1 0_0 # Python >= 3.6 is required ^ SyntaxError: invalid syntax