Open anders-kiaer opened 2 years ago
I really like this idea. I just put together a simple (but working) prototype implementation inspired by your code. So far, the syntax looks like this,
from dash_extensions.enrich import T, DashProxy, callback, html
@callback()
def hello(n_clicks: T[int, "btn", "n_clicks"]) -> T[str, "log", "children"]:
return "Hello world!"
app = DashProxy(prevent_initial_callbacks=True)
app.layout = html.Div([html.Button("Click me", id="btn"), html.Div(id="log")])
if __name__ == '__main__':
app.run_server()
where T
is the import name for Annotated
(where "T" is short for "Type", it could also just have been "A", or maybe "P" for "Prop"). My immediate idea was to create Ouput
/Input
/State
classes by subclassing Annotated
, but it seems this is not possible. What do you think, @anders-kiaer ? Do you have any ideas for improvements? :)
Another option would be to use a syntax closer to the current one, e.g. something like
from dash_extensions.enrich import DashProxy, callback, html, Input, Output
@callback
def hello(n_clicks: Input("btn", "n_clicks")) -> Output("log", "children"):
return "Hello world!"
app = DashProxy(prevent_initial_callbacks=True)
app.layout = html.Div([html.Button("Click me", id="btn"), html.Div(id="log")])
if __name__ == '__main__':
app.run_server()
This approach doesn't allow the use of actual type annotations though, which might be a drawback. On the other hand, native Dash doesn't allow complex types as input/output for callbacks, so it might not be so bad after all.
I really like this idea. I just put together a simple (but working) prototype implementation inspired by your code.
ππ
Do you have any ideas for improvements? :)
Overall I like the syntax and think using type hint annotations improves readability. I'm not sure if the following are ideas, maybe more questions:
Input
/State
) and Output
are clearly distinguished by being input and output type hints of the callback function. How do we best distinguish between Input
and State
within the input arguments?from dash_extensions.enrich import T
- did you encounter issue with e.g. from typing import Annotated as A
from std.lib?Reading the Python standard library documentation of typing.Annotated
, they have examples of using typing.Annoted[sometype, SomeClass(initval)]
, maybe because it is easier to distinguish then with isinstance
(as they also use as example) should the end user have other use cases for annotating the arguments, in addition to dash
(id, prop)
specification (in pydantic
they have some discussion on e.g. argument text descriptions as annotations). E.g.:
from dash.dependencies import Prop
@callback
def hello(
some_input: T[int, Prop("id", "prop")],
some_state: T[int, Prop("id", "prop", trigger=False)],
) -> T[str, Prop("id", "prop")]:
return "Hello world!"
On the other hand, native Dash doesn't allow complex types as input/output for callbacks, so it might not be so bad after all.
My hope is that it will change after #1786 - and then it would be nice to able to use the full power of type hint annotations. π
One option (combining the class approach above and also reuse existing Input
/State
/Output
) could be
@callback
def hello(n_clicks: A[sometype, Input("btn", "n_clicks")]) -> A[sometype, Output("log", "children")]:
return "Hello world!"
but it feels more verbose/explicit than necessary (Output
is already clearly an output by being the returned type of the function).
I have done another (small) iteration of the syntax, partly based on your comments, @anders-kiaer . My working example now looks like this,
from dash_extensions.enrich import DashProxy, callback, html, dcc, prop
@callback
def hello(n_clicks: prop("btn", "n_clicks", int), # the type definition "int" is optional
name: prop("name", "value", trigger=False)) -> prop("log", "children"):
return f"Hello {name}! (click count is {n_clicks})"
app = DashProxy(prevent_initial_callbacks=True)
app.layout = html.Div([
dcc.Input(placeholder="Enter your name here", id="name"),
html.Button("Click me!", id="btn"),
html.Div(id="log")
])
if __name__ == '__main__':
app.run_server()
A few notes on the syntax,
Input
/Output
/State
objects are replaced by a common prop
function prop
function are component id and component property (both mandatory), the third argument is an optional type definition (which just defaults to any
)Input
, but can be changed to State
by passing trigger=False
Output
, but can be changes to ServersideOutput
by passing serverside=True
You should be able to try out the syntax with the following rc release,
https://pypi.org/project/dash-extensions/0.0.67rc2/
I haven't tested much more than the example above, so expect dragons :)
Hey @anders-kiaer and @emilhe
I'd be interested to hear your feedback on #1952 Improved callback_context
- especially the section "Bonus 1: Simplified callback function signatures" section
Is your feature request related to a problem? Please describe. When creating complex Dash dashbords/callbacks, there can be a long list of input/state/output. We in some cases have seen things of the size of:
π± Both during development, but also code review/maintenance, there is mental overhead with respect to seeing which
(id, prop)
pair belongs to which named argument in the function. This has gotten a bit better with https://dash.plotly.com/flexible-callback-signatures, but the underlying problem with(id, prop)
and named argument in the function being defined in two different lines remains.Describe the solution you'd like Utilize the Python 3+ typing syntax to annotate the
(id, prop)
closer to the argument. By using that we at the same time can avoid explicitly statingOutput
as that is already explicit by being defined as the returned type(s) of the function. The only thing to differentiate between isInput
/State
which could be done by some extra annotation tag. E.g. something likeAnother benefit is that we encourage Dash app developers to type hint their callback functions which again helps IDEs and
mypy
detect bugs (related to #1786).Additional context
See https://docs.python.org/3/library/typing.html#typing.Annotated for documentation on
typing.Annotated
(backported to earlier Python 3 versions intyping_extensions
).Related to #1748 and #1786, but implementation is independent of those.
PoC code showing how type annotations potentially can be transformed into the
Input
/Output
/State
when callbacks are registered/decorated: