Test file (test.py):

print(set(x for x in range(2),))

Python runs it nicely:

% python2 test.py 
set([0, 1])
% python3 test.py
{0, 1}

2to3 parser (on both Python 2.7.11 and 3.5.2) chokes on it though:

% /usr/local/Cellar/python/2.7.11/Frameworks/Python.framework/Versions/2.7/bin/2to3 test.py 
RefactoringTool: Skipping optional fixer: buffer
RefactoringTool: Skipping optional fixer: idioms
RefactoringTool: Skipping optional fixer: set_literal
RefactoringTool: Skipping optional fixer: ws_comma
RefactoringTool: Can't parse test.py: ParseError: bad input: type=8, value=u')', context=('', (1, 30))
RefactoringTool: No files need to be modified.
RefactoringTool: There was 1 error:
RefactoringTool: Can't parse test.py: ParseError: bad input: type=8, value=u')', context=('', (1, 30))

% /usr/local/Cellar/python3/3.5.2/Frameworks/Python.framework/Versions/3.5/bin/2to3 test.py 
RefactoringTool: Skipping optional fixer: buffer
RefactoringTool: Skipping optional fixer: idioms
RefactoringTool: Skipping optional fixer: set_literal
RefactoringTool: Skipping optional fixer: ws_comma
RefactoringTool: Can't parse test.py: ParseError: bad input: type=8, value=')', context=('', (1, 30))
RefactoringTool: No files need to be modified.
RefactoringTool: There was 1 error:
RefactoringTool: Can't parse test.py: ParseError: bad input: type=8, value=')', context=('', (1, 30))


For reference: https://github.com/smarkets/flake8-strict/issues/9 (project using lib2to3 parser)