Some of the tests for lib2to3 write into folders which are protected in an installed Python. This means that regression tests fail when run on an installed Python, even though they run wihtout these errors on a source build. I think writes should be done into temp files, so that you can run regressions on installed Pythons.

Example failure:

======================================================================
ERROR: test_refactor_file (lib2to3.tests.test_refactor.TestRefactoringTool)
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Traceback (most recent call last):
  File "/usr/local/lib/python3.3/lib2to3/tests/test_refactor.py", line 190, in check_file_refactoring
    rt.refactor_file(test_file, True)
  File "/usr/local/lib/python3.3/lib2to3/refactor.py", line 353, in refactor_file
    write=write, encoding=encoding)
  File "/usr/local/lib/python3.3/lib2to3/refactor.py", line 518, in processed_file
    self.write_file(new_text, filename, old_text, encoding)
  File "/usr/local/lib/python3.3/lib2to3/refactor.py", line 530, in write_file
    f = _open_with_encoding(filename, "w", encoding=encoding)
IOError: [Errno 13] Permission denied: '/usr/local/lib/python3.3/lib2to3/tests/data/fixers/parrot_example.py'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.3/lib2to3/tests/test_refactor.py", line 200, in test_refactor_file
    self.check_file_refactoring(test_file, _DEFAULT_FIXERS)
  File "/usr/local/lib/python3.3/lib2to3/tests/test_refactor.py", line 194, in check_file_refactoring
    with open(test_file, "wb") as fp:
IOError: [Errno 13] Permission denied: '/usr/local/lib/python3.3/lib2to3/tests/data/fixers/parrot_example.py'