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## Events
Custom events can be added to guizero widgets to call functions when the user takes the following actions:
- when clicked - `when_clicked`
- when the left mouse button is pressed - `when_left_button_pressed`
- when the left mouse button is released - `when_left_button_released`
- when the right mouse button is pressed - `when_right_button_pressed`
- when the right mouse button is released - `when_right_button_released`
- when a key is pressed - `when_key_pressed`
- when a key is released - `when_key_released`
- when the mouse enters a widget - `when_mouse_enters`
- when the mouse leaves a widget - `when_mouse_leaves`
- when the mouse is dragged across a widget - `when_mouse_dragged`
Events are set by assigning them to a function:
```python
def do_this():
print("The widget was clicked")
widget.when_clicked = do_this
```
### Event Data
The function which is called can also accept a parameter and will be passed data about the event which occured.
The event data returned has:
- `widget` - the guizero widget which raised the event
- `tk_event` - the [tkinter event object](http://effbot.org/tkinterbook/tkinter-events-and-bindings.htm)
- `key` - the key which raised the event
- `x` - the mouse's x position relative to the widget when the event occured
- `y` - the mouse's y position relative to the widget when the event occured
- `display_x` - the mouse's x position on the display when the event occured
- `display_y` - the mouse's y position on the display when the event occured
```python
def clicked(event_data):
print("widget clicked = " + event_data.widget)
print("mouse position = " + event_data.x + "." + event_data.y)
widget.when_clicked = clicked
```
### Example
Highlight a text box widget by changing its background color (`bg`) when the mouse is hovering over it.
```python
from guizero import App, TextBox
def highlight():
text_box.bg = "lightblue"
def lowlight():
text_box.bg = "white"
app = App()
text_box = TextBox(app)
# When the mouse enters the TextBox
text_box.when_mouse_enters = highlight
# When the mouse leaves the TextBox
text_box.when_mouse_leaves = lowlight
app.display()
```
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