# PyQt4 and Qt v5

## Building Against Qt v5

PyQt4 can be built against Qt v5 in exactly the same way that it is built against Qt v4. However only a Qt v4 compatible subset of Qt v5 is supported, specifically:

- any classes added in Qt v5 are not supported
- any new features added in Qt v5 to classes that exist in Qt v4 are supported
- any features that are marked as deprecated in Qt v5 are supported.

Qt v5 handles connections to signals with optional arguments in a slightly different way than Qt v4. PyQt4 works around this as best it can but cannot do so in the case where signals that have optional arguments in Qt v5 (but not in Qt v4) are emitted using old-style signals (i.e. using `QObject.emit()`). Instead you should use new-style signals (i.e. use the `emit()` method of the bound signal).

The `--no-deprecated` option to PyQt4’s configure.py can be used to disable the support for the deprecated features. This can be useful in the porting of PyQt4 applications to PyQt5.