# Devices and Properties

`pymmcore-plus` offers two classes that provide a more *object-oriented* interface to common operations and queries performed on devices and their properties.

In the original `CMMCore` API, there are a lot of methods that accept a `deviceLabel` string as the first argument (and perhaps additional arguments) and query something about that device (e.g. `getDeviceLibrary`, `getDeviceType`, `waitForDevice`, etc...). In `pymmcore-plus`, the `Device` class acts as a "view" onto a specific device. You pass the `deviceLabel` once (to the constructor), and these become methods that no longer need it.

Similarly, there are many methods in the `CMMCore` API that require both a device label and a device property name, and query or modify that property (e.g. `isPropertySequenceable`, `getProperty`, `isPropertyReadOnly`, etc...). Here, the `DeviceProperty` class acts as a "view" onto a specific device property, with an object-oriented interface to these methods.

```python
from pymmcore_plus import CMMCorePlus

core = CMMCorePlus()
core.loadSystemConfiguration()  # demo config

camera = core.getDeviceObject("Camera")
print(camera.type(), camera.library())  # Camera DemoCamera

exposure = camera.getPropertyObject("Exposure")
exposure.value = 42
print(exposure.value, exposure.isReadOnly(), exposure.range())  # 42.0 False (0.0, 10000.0)
```

To loop over the loaded devices or properties (optionally filtered by type, label, etc...), use `iterDevices` and `iterProperties`, which yield these same objects:

```python
from pymmcore_plus import DeviceType

[dev.label for dev in core.iterDevices(DeviceType.Stage)]  # ['Z']
[prop.name for prop in core.iterProperties(device_label="Camera", has_limits=True)]
```

See `Device`, `DeviceProperty` and `DeviceAdapter` (the same idea, for a device adapter library) for the full API.

## Property info

`DeviceProperty.dict()` returns everything about a property at once. Continuing the example above:

```python
>>> exposure.dict()
{'valid': True,
 'value': 42.0,
 'type': 'number',
 'device_type': 'CameraDevice',
 'read_only': False,
 'sequenceable': False,
 'sequence_max_length': None,
 'pre_init': False,
 'range': (0.0, 10000.0),
 'allowed_values': ()}
```

(`range` is `None` for properties without limits, and `allowed_values` lists the choices for properties that have them, like the camera's `Binning`.)

## Temporarily changing settings

You may want to temporarily set something on the core (for example `core.setAutoShutter(False)` when writing an [MDA engine](<https://pymmcore-plus.github.io/pymmcore-plus/guides/custom_engine/index.md>)) and put it back afterwards. For this case you can use the convenience method `CMMCorePlus.setContext`:

```python
with core.setContext(exposure=100, autoShutter=False):
    print(core.getExposure(), core.getAutoShutter())  # 100.0 False
    core.snapImage()

print(core.getExposure(), core.getAutoShutter())  # back to the original values
```

This works for any name that has matching `get<Name>` and `set<Name>` methods on the core (e.g. `exposure`, `autoShutter`, `shutterOpen`, `channelGroup`, etc...). The original values are restored when the `with` block exits, even if an exception was raised inside it.