The following code gives a SyntaxError in 3.10, but used to work fine before (I have tested it in 2.7, 3.8, 3.9):

    1not in [2, 3]

It seems to be only the `not in` syntax which is affected; all other keywords still work correctly:

    1in [2, 3]
    1or 2
    1and 2
    1if 1else 1
    1is 1

I know this syntax is deprecated in 3.10 (bpo43833), but it still needs to work for now, so that old code written like this can keep working.