For production Dash apps, Dash Core Components styling and layout
should be managed with Dash Enterprise Design Kit.
An example of a default dropdown without any extra properties.
import dash
import dash_html_components as html
import dash_core_components as dcc
external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']
app = dash.Dash(__name__, external_stylesheets=external_stylesheets)
app.layout = html.Div([
dcc.Dropdown(
id='demo-dropdown',
options=[
{'label': 'New York City', 'value': 'NYC'},
{'label': 'Montreal', 'value': 'MTL'},
{'label': 'San Francisco', 'value': 'SF'}
],
value='NYC'
),
html.Div(id='dd-output-container')
])
@app.callback(
dash.dependencies.Output('dd-output-container', 'children'),
[dash.dependencies.Input('demo-dropdown', 'value')])
def update_output(value):
return 'You have selected "{}"'.format(value)
if __name__ == '__main__':
app.run_server(debug=True)
A dropdown component with the multi property set to True will allow the user to select more than one value at a time.
import dash_core_components as dcc
dcc.Dropdown(
options=[
{'label': 'New York City', 'value': 'NYC'},
{'label': 'Montreal', 'value': 'MTL'},
{'label': 'San Francisco', 'value': 'SF'}
],
value=['MTL', 'NYC'],
multi=True
)
The searchable property is set to True by default on all Dropdown components. To prevent searching the dropdown value, just set the searchable property to False. Try searching for ‘New York’ on this dropdown below and compare it to the other dropdowns on the page to see the difference.
import dash_core_components as dcc
dcc.Dropdown(
options=[
{'label': 'New York City', 'value': 'NYC'},
{'label': 'Montreal', 'value': 'MTL'},
{'label': 'San Francisco', 'value': 'SF'}
],
searchable=False
)
The clearable property is set to True by default on all Dropdown components. To prevent the clearing of the selected dropdown value, just set the clearable property to False
import dash_core_components as dcc
dcc.Dropdown(
options=[
{'label': 'New York City', 'value': 'NYC'},
{'label': 'Montreal', 'value': 'MTL'},
{'label': 'San Francisco', 'value': 'SF'},
],
value='MTL',
clearable=False
)
The placeholder property allows you to define default text shown when no value is selected.
import dash_core_components as dcc
dcc.Dropdown(
options=[
{'label': 'New York City', 'value': 'NYC'},
{'label': 'Montreal', 'value': 'MTL'},
{'label': 'San Francisco', 'value': 'SF'}
],
placeholder="Select a city",
)
To disable the dropdown just set disabled=True.
import dash_core_components as dcc
dcc.Dropdown(
options=[
{'label': 'New York City', 'value': 'NYC'},
{'label': 'Montreal', 'value': 'MTL'},
{'label': 'San Francisco', 'value': 'SF'}
],
disabled=True
)
To disable a particular option inside the dropdown menu, set the disabled property in the options.
import dash_core_components as dcc
dcc.Dropdown(
options=[
{'label': 'New York City', 'value': 'NYC', 'disabled': True},
{'label': 'Montreal', 'value': 'MTL'},
{'label': 'San Francisco', 'value': 'SF', 'disabled': True}
],
)
This is an example on how to update the options on the server depending on the search terms the user types. For example purpose the options are empty on first load, as soon as you start typing they will be loaded with the corresponding values.
import dash
from dash.exceptions import PreventUpdate
import dash_html_components as html
import dash_core_components as dcc
external_stylesheets = ["https://codepen.io/chriddyp/pen/bWLwgP.css"]
options = [
{"label": "New York City", "value": "NYC"},
{"label": "Montreal", "value": "MTL"},
{"label": "San Francisco", "value": "SF"},
]
app = dash.Dash(__name__, external_stylesheets=external_stylesheets)
app.layout = html.Div(
[
html.Label(["Single dynamic Dropdown", dcc.Dropdown(id="my-dynamic-dropdown")]),
html.Label(
[
"Multi dynamic Dropdown",
dcc.Dropdown(id="my-multi-dynamic-dropdown", multi=True),
]
),
]
)
@app.callback(
dash.dependencies.Output("my-dynamic-dropdown", "options"),
[dash.dependencies.Input("my-dynamic-dropdown", "search_value")],
)
def update_options(search_value):
if not search_value:
raise PreventUpdate
return [o for o in options if search_value in o["label"]]
@app.callback(
dash.dependencies.Output("my-multi-dynamic-dropdown", "options"),
[dash.dependencies.Input("my-multi-dynamic-dropdown", "search_value")],
[dash.dependencies.State("my-multi-dynamic-dropdown", "value")],
)
def update_multi_options(search_value, value):
if not search_value:
raise PreventUpdate
# Make sure that the set values are in the option list, else they will disappear
# from the shown select list, but still part of the `value`.
return [
o for o in options if search_value in o["label"] or o["value"] in (value or [])
]
if __name__ == "__main__":
app.run_server(debug=True)
Access this documentation in your Python terminal with:
```pythonhelp(dash_core_components.Dropdown)
```Our recommended IDE for writing Dash apps is Dash Enterprise’s
Data Science Workspaces,
which has typeahead support for Dash Component Properties.
Find out if your company is using
Dash Enterprise.
id (string; optional):
The ID of this component, used to identify dash components in
callbacks. The ID needs to be unique across all of the components
in an app.
className (string; optional):
className of the dropdown element.
clearable (boolean; default True):
Whether or not the dropdown is “clearable”, that is, whether or
not a small “x” appears on the right of the dropdown that
removes the selected value.
disabled (boolean; default False):
If True, this dropdown is disabled and the selection cannot be
changed.
loading_state (dict; optional):
Object that holds the loading state object coming from
dash-renderer.
loading_state is a dict with keys:
component_name (string; optional):
Holds the name of the component that is loading.
is_loading (boolean; optional):
Determines if the component is loading or not.
prop_name (string; optional):
Holds which property is loading.
multi (boolean; default False):
If True, the user can select multiple values.
optionHeight (number; default 35):
height of each option. Can be increased when label lengths would
wrap around.
options (list of dicts; optional):
An array of options {label: [string|number], value:
[string|number]}, an optional disabled field can be used for each
option.
options is a list of dicts with keys:
disabled (boolean; optional):
If True, this option is disabled and cannot be selected.
label (string | number; required):
The dropdown’s label.
title (string; optional):
The HTML ‘title’ attribute for the option. Allows for
information on hover. For more information on this attribute,
see
https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/title.
value (string | number; required):
The value of the dropdown. This value corresponds to the items
specified in the value property.
persisted_props (list of a value equal to: ‘value’s; default \['value'\]):
Properties whose user interactions will persist after refreshing
the component or the page. Since only value is allowed this prop
can normally be ignored.
persistence (boolean | string | number; optional):
Used to allow user interactions in this component to be persisted
when the component - or the page - is refreshed. If persisted is
truthy and hasn’t changed from its previous value, a value that
the user has changed while using the app will keep that change, as
long as the new value also matches what was given originally.
Used in conjunction with persistence_type.
persistence_type (a value equal to: ‘local’, ‘session’, ‘memory’; default 'local'):
Where persisted user changes will be stored: memory: only kept in
memory, reset on page refresh. local: window.localStorage, data is
kept after the browser quit. session: window.sessionStorage, data
is cleared once the browser quit.
placeholder (string; optional):
The grey, default text shown when no option is selected.
search_value (string; optional):
The value typed in the DropDown for searching.
searchable (boolean; default True):
Whether to enable the searching feature or not.
style (dict; optional):
Defines CSS styles which will override styles previously set.
value (string | number | list of string | numbers; optional):
The value of the input. If multi is False (the default) then
value is just a string that corresponds to the values provided in
the options property. If multi is True, then multiple values
can be selected at once, and value is an array of items with
values corresponding to those in the options prop.