False positives when detecting generalized unpacking and bytes formatting

When I try the latest version of vermin (from the master branch, with recent implemenation of generalized unpacking and bytes formatting detection) against some code of my projects, I noticed some false positives when detecting generalized unpacking and bytes formatting.

Case 1:

d = {'a': 'b'}
dict(**d)

Expected: No issues detected (Minimum required versions: ~2, ~3)

Actual: L2: generalized unpacking requires 3.5+

Case 2:

'%x' % 66

Expected: No issues detected (Minimum required versions: ~2, ~3)

Actual: L1: bytes `%` formatting requires 3.5+ (or 2.6+ as `str` synonym)

In this commit, why is isinstance(node.left, ast.Str) necessary? Is it because of some compatibility reasons? b'' is 2.6+, but '%x' % 66 is ~2, ~3.

[gousaiyang]

Looks good. It is fine to close this issue now.

[gousaiyang]

Here are some test results under Python 3.4. Invalid cases should be regarded as generalized unpacking (they are valid on 3.5+) but valid cases are not.

Unpacking in literals (tuple, list, set, and dictionary displays) is always invalid in Python 3.4: (*(1,),) -> invalid (*(1, 2),) -> invalid (0, *(1, 2)) -> invalid (*(1, 2), 3) -> invalid (0, *(1, 2), 3) -> invalid (*(1, 2), *(3, 4)) -> invalid [*[1]] -> invalid [*[1, 2]] -> invalid [0, *[1, 2]] -> invalid [*[1, 2], 3] -> invalid [0, *[1, 2], 3] -> invalid [*[1, 2], *[3, 4]] -> invalid {*{1}} -> invalid {*{1, 2}} -> invalid {0, *{1, 2}} -> invalid {*{1, 2}, 3} -> invalid {0, *{1, 2}, 3} -> invalid {*{1, 2}, *{3, 4}} -> invalid {**{1: 1}} -> invalid {**{1: 1, 2: 2}} -> invalid {0: 0, **{1: 1, 2: 2}} -> invalid {**{1: 1, 2: 2}, 3: 3} -> invalid {0: 0, **{1: 1, 2: 2}, 3: 3} -> invalid {**{1: 1, 2: 2}, **{3: 3, 4: 4}} -> invalid

In Python 3.4, unpacking in function call parameter list is only allowed at the end of the parameter list, and only one unpacking is allowed. Unpacking in positional argument list and keyword argument list are processed separately: print(*(1,)) -> valid print(*(1, 2)) -> valid print(0, *(1, 2)) -> valid print(*(1, 2), 3) -> invalid print(0, *(1, 2), 3) -> invalid print(*(1, 2), *(3, 4)) -> invalid dict(**{"b": 1}) -> valid dict(**{"b": 1, "c": 2}) -> valid dict(a=0, **{"b": 1, "c": 2}) -> valid dict(**{"b": 1, "c": 2}, d=3) -> invalid dict(a=0, **{"b": 1, "c": 2}, d=3) -> invalid dict(**{"b": 1, "c": 2}, **{"d": 3, "e": 4}) -> invalid foo(0, *(1, 2), a=1, **{"b": 2, "c": 3}) -> valid foo(0, *(1, 2), 3, a=1, **{"b": 2, "c": 3}) -> invalid foo(0, *(1, 2), a=1, **{"b": 2, "c": 3}, d=4) -> invalid