# Troubleshooting Qt and Widgets

For problems with the core itself (finding Micro-Manager, loading device adapters), see [Troubleshooting](<https://pymmcore-plus.github.io/pymmcore-plus/troubleshooting/index.md>) for pymmcore-plus.

## No Qt bindings

```sh
qtpy.QtBindingsNotFoundError: No Qt bindings could be found
```

If you get an error similar to the one above, it means that you did not install one of the necessary [PyQt](<https://riverbankcomputing.com/software/pyqt/>) or [PySide](<https://www.qt.io/qt-for-python>) libraries. Install `pymmcore-widgets` with an extra that brings one along:

```sh
pip install "pymmcore-widgets[PyQt6]"  # or "pymmcore-widgets[PySide6]"
```

See [Installing a Qt backend](<https://pymmcore-plus.github.io/pymmcore-widgets/getting_started/#installing-a-qt-backend>) for how to choose.

## "no matches found" when installing

```sh
zsh: no matches found: pymmcore-widgets[PyQt6]
```

zsh (the default shell on macOS) treats the square brackets as a file pattern. Put quotes around the package name: `pip install "pymmcore-widgets[PyQt6]"`.

## Must construct a QApplication

```text
QWidget: Must construct a QApplication before a QWidget
```

... followed by Python crashing. Every Qt program needs a `QApplication`, and it must exist before you create any widget. Create it first thing (and create it *before* the `CMMCorePlus`, too, for the reasons explained in [Qt integration](<https://pymmcore-plus.github.io/pymmcore-plus/examples/integration-with-qt/#create-the-qapplication-first>)):

```python
from qtpy.QtWidgets import QApplication

app = QApplication([])
# ... now create the core and the widgets
app.exec()
```

## The widgets don't follow my script

If you change something from your own code (`core.setExposure(50)`, say) and a widget doesn't update, the widget is probably connected to a different core. Widgets use the global `CMMCorePlus.instance()` unless you pass `mmcore=`, so a core you created with `CMMCorePlus()` is a separate object, with its own devices and its own events. Either use `CMMCorePlus.instance()` in your script, or pass your core to each widget: `ExposureWidget(mmcore=my_core)`.

Also check that the widget uses a core at all (the sequence editors, like `ChannelTable` and `ZPlanWidget`, don't). See [Choosing a core](<https://pymmcore-plus.github.io/pymmcore-widgets/getting_started/#choosing-a-core>).

## The GUI freezes

Anything that blocks the main thread (the one running `app.exec()`) freezes the whole GUI until it returns: a long `core.snapImage()`, a slow stage move, a `time.sleep()` in a callback, etc... Run long operations in a thread instead. `CMMCorePlus.run_mda` already does this for you. See [Qt integration](<https://pymmcore-plus.github.io/pymmcore-plus/examples/integration-with-qt/index.md>) for an example.

Please [open an issue](<https://github.com/pymmcore-plus/pymmcore-widgets/issues>) if you run into something that isn't covered here.