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# Known limitations

`futurize` and `pasteurize` are useful to automate much of the work of porting, particularly the boring repetitive text substitutions. They also help to flag which parts of the code require attention.

Nevertheless, `futurize` and `pasteurize` are still incomplete and make some mistakes, like 2to3, on which they are based. Please report bugs on GitHub. Contributions to the `lib2to3`-based fixers for `futurize` and `pasteurize` are particularly welcome! Please see Contributing.

`futurize` doesn’t currently make the following change automatically:

1. Strings containing `\U` produce a `SyntaxError` on Python 3. An example is:

       s = 'C:\Users'.

   Python 2 expands this to `s = 'C:\\Users'`, but Python 3 requires a raw prefix (`r'...'`). This also applies to multi-line strings (including multi-line docstrings).

Also see the tests in `future/tests/test_futurize.py` marked `@expectedFailure` or `@skip` for known limitations.

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