limitations of the future module and differences between Py2 and Py3 that are not (yet) handled — Python-Future documentation

# limitations of the `future` module and differences between Py2 and Py3 that are not (yet) handled

The following attributes on functions in Python 3 are not provided in Python 2.7:

__func__: see six.get_method_function() __self__: see six.get_method_self() __self__.__class__

## Limitations of the `futurize` script

The `futurize` script is not yet mature; like `2to3`, on which it is based, it makes mistakes. Nevertheless, it should be useful for automatically performing a lot of the repetitive code-substitution tasks when porting from Py2 to Py2/3.

Some new Python 3.3 features that cause SyntaxErrors on earlier versions are not currently handled by the `futurize` script. This includes:

- `yield ... from` syntax for generators in Py3.3

- `raise ... from` syntax for exceptions. (This is simple to fix manually by creating a temporary variable.)

Also:

- Usage of `file('myfile', 'w')` as a synonym for `open` doesn’t seem to be converted currently.

- `isinstance(var, basestring)` should sometimes be converted to `isinstance(var, str) or isinstance(var, bytes)`, or sometimes simply `isinstance(var, str)`, depending on the context. Currently it is always converted to `isinstance(var, str)`.

- Caveats with bytes indexing!:

      b'\x00'[0] != 0
      b'\x01'[0] != 1

  `futurize` does not yet wrap all byte-string literals in a `bytes()` call. This is on the to-do list. See bytes for more information.

## Notes

- Ensure you are using new-style classes on Py2. Py3 doesn’t require inheritance from `object` for this, but Py2 does. `pasteurize` adds this back in automatically, but ensure you do this too when writing your classes, otherwise weird breakage when e.g. calling `super()` may occur.