Single input

CHANGELOG.md

@@ -2,10 +2,13 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org/).
 
-## Unreleased
+## [UNRELEASED]
 ### Added
 - [#1315](https://github.com/plotly/dash/pull/1315) Add `update_title` parameter to set or disable the "Updating...." document title during updates. Closes [#856](https://github.com/plotly/dash/issues/856) and [#732](https://github.com/plotly/dash/issues/732)
 
+### Changed
+- [#1180](https://github.com/plotly/dash/pull/1180) `Input`, `Output`, and `State` in callback definitions don't need to be in lists. You still need to provide `Output` items first, then `Input` items, then `State`, and the list form is still supported. In particular, if you want to return a single output item wrapped in a length-1 list, you should still wrap the `Output` in a list. This can be useful for procedurally-generated callbacks.
+
 ## [1.13.4] - 2020-06-25
 ### Fixed
 - [#1310](https://github.com/plotly/dash/pull/1310) Fix a regression since 1.13.0 preventing more than one loading state from being shown at a time.

dash/_validate.py

@@ -2,73 +2,76 @@
 import re
 
 from .development.base_component import Component
-from .dependencies import Input, Output, State
 from . import exceptions
 from ._utils import patch_collections_abc, _strings, stringify_id
 
 
-def validate_callback(output, inputs, state):
+def validate_callback(output, inputs, state, extra_args, types):
+    Input, Output, State = types
+    if extra_args:
+        if not isinstance(extra_args[0], (Output, Input, State)):
+            raise exceptions.IncorrectTypeException(
+                """
+                Callback arguments must be `Output`, `Input`, or `State` objects,
+                optionally wrapped in a list or tuple. We found (possibly after
+                unwrapping a list or tuple):
+                {}
+                """.format(
+                    repr(extra_args[0])
+                )
+            )
+
+        raise exceptions.IncorrectTypeException(
+            """
+            In a callback definition, you must provide all Outputs first,
+            "then all Inputs, then all States. Found this out of order:
+            {}
+            """.format(
+                repr(extra_args)
+            )
+        )
+
     is_multi = isinstance(output, (list, tuple))
 
     outputs = output if is_multi else [output]
 
-    for args, cls in [(outputs, Output), (inputs, Input), (state, State)]:
-        validate_callback_args(args, cls)
+    for args in [outputs, inputs, state]:
+        for arg in args:
+            validate_callback_arg(arg)
 
 
-def validate_callback_args(args, cls):
-    name = cls.__name__
-    if not isinstance(args, (list, tuple)):
+def validate_callback_arg(arg):
+    if not isinstance(getattr(arg, "component_property", None), _strings):
         raise exceptions.IncorrectTypeException(
             """
-            The {} argument `{}` must be a list or tuple of
-            `dash.dependencies.{}`s.
+            component_property must be a string, found {!r}
             """.format(
-                name.lower(), str(args), name
+                arg.component_property
             )
         )
 
-    for arg in args:
-        if not isinstance(arg, cls):
-            raise exceptions.IncorrectTypeException(
-                """
-                The {} argument `{}` must be of type `dash.dependencies.{}`.
-                """.format(
-                    name.lower(), str(arg), name
-                )
-            )
-
-        if not isinstance(getattr(arg, "component_property", None), _strings):
-            raise exceptions.IncorrectTypeException(
-                """
-                component_property must be a string, found {!r}
-                """.format(
-                    arg.component_property
-                )
-            )
-
-        if hasattr(arg, "component_event"):
-            raise exceptions.NonExistentEventException(
-                """
-                Events have been removed.
-                Use the associated property instead.
-                """
-            )
+    if hasattr(arg, "component_event"):
+        raise exceptions.NonExistentEventException(
+            """
+            Events have been removed.
+            Use the associated property instead.
+            """
+        )
 
-        if isinstance(arg.component_id, dict):
-            validate_id_dict(arg)
+    if isinstance(arg.component_id, dict):
+        validate_id_dict(arg)
 
-        elif isinstance(arg.component_id, _strings):
-            validate_id_string(arg)
+    elif isinstance(arg.component_id, _strings):
+        validate_id_string(arg)
 
-        else:
-            raise exceptions.IncorrectTypeException(
-                """
-                component_id must be a string or dict, found {!r}
-                """.format(
-                    arg.component_id
-                )
+    else:
+        raise exceptions.IncorrectTypeException(
+            """
+            component_id must be a string or dict, found {!r}
+            """.format(
+                arg.component_id
             )
+        )
 
 
 def validate_id_dict(arg):

dash/dash.py

@@ -23,6 +23,7 @@
 
 from .fingerprint import build_fingerprint, check_fingerprint
 from .resources import Scripts, Css
+from .dependencies import handle_callback_args
 from .development.base_component import ComponentRegistry
 from .exceptions import PreventUpdate, InvalidResourceError, ProxyError
 from .version import __version__
@@ -830,7 +831,6 @@ def _insert_callback(self, output, inputs, state, prevent_initial_call):
         if prevent_initial_call is None:
             prevent_initial_call = self.config.prevent_initial_callbacks
 
-        _validate.validate_callback(output, inputs, state)
         callback_id = create_callback_id(output)
         callback_spec = {
             "output": callback_id,
@@ -847,9 +847,7 @@ def _insert_callback(self, output, inputs, state, prevent_initial_call):
 
         return callback_id
 
-    def clientside_callback(
-        self, clientside_function, output, inputs, state=(), prevent_initial_call=None
-    ):
+    def clientside_callback(self, clientside_function, *args, **kwargs):
         """Create a callback that updates the output by calling a clientside
         (JavaScript) function instead of a Python function.
 
@@ -914,6 +912,7 @@ def clientside_callback(
         not to fire when its outputs are first added to the page. Defaults to
         `False` unless `prevent_initial_callbacks=True` at the app level.
         """
+        output, inputs, state, prevent_initial_call = handle_callback_args(args, kwargs)
         self._insert_callback(output, inputs, state, prevent_initial_call)
 
         # If JS source is explicitly given, create a namespace and function
@@ -945,18 +944,23 @@ def clientside_callback(
             "function_name": function_name,
         }
 
-    def callback(self, output, inputs, state=(), prevent_initial_call=None):
+    def callback(self, *_args, **_kwargs):
         """
         Normally used as a decorator, `@app.callback` provides a server-side
-        callback relating the values of one or more `output` items to one or
-        more `input` items which will trigger the callback when they change,
-        and optionally `state` items which provide additional information but
+        callback relating the values of one or more `Output` items to one or
+        more `Input` items which will trigger the callback when they change,
+        and optionally `State` items which provide additional information but
         do not trigger the callback directly.
 
         The last, optional argument `prevent_initial_call` causes the callback
         not to fire when its outputs are first added to the page. Defaults to
         `False` unless `prevent_initial_callbacks=True` at the app level.
+
+
         """
+        output, inputs, state, prevent_initial_call = handle_callback_args(
+            _args, _kwargs
+        )
         callback_id = self._insert_callback(output, inputs, state, prevent_initial_call)
         multi = isinstance(output, (list, tuple))
 
@@ -1028,7 +1032,7 @@ def dispatch(self):
 
         response = flask.g.dash_response = flask.Response(mimetype="application/json")
 
-        args = inputs_to_vals(inputs) + inputs_to_vals(state)
+        args = inputs_to_vals(inputs + state)
 
         func = self.callback_map[output]["callback"]
         response.set_data(func(*args, outputs_list=outputs_list))

dash/dependencies.py

@@ -1,5 +1,7 @@
 import json
 
+from ._validate import validate_callback
+
 
 class _Wildcard:  # pylint: disable=too-few-public-methods
     def __init__(self, name):
@@ -133,3 +135,40 @@ def __init__(self, namespace=None, function_name=None):
 
     def __repr__(self):
         return "ClientsideFunction({}, {})".format(self.namespace, self.function_name)
+
+
+def extract_callback_args(args, kwargs, name, type_):
+    """Extract arguments for callback from a name and type"""
+    parameters = kwargs.get(name, [])
+    if not parameters:
+        while args and isinstance(args[0], type_):
+            parameters.append(args.pop(0))
+    return parameters
+
+
+def handle_callback_args(args, kwargs):
+    """Split args into outputs, inputs and states"""
+    prevent_initial_call = kwargs.get("prevent_initial_call", None)
+    if prevent_initial_call is None and args and isinstance(args[-1], bool):
+        prevent_initial_call = args.pop()
+
+    # flatten args, to support the older syntax where outputs, inputs, and states
+    # each needed to be in their own list
+    flat_args = []
+    for arg in args:
+        flat_args += arg if isinstance(arg, (list, tuple)) else [arg]
+
+    outputs = extract_callback_args(flat_args, kwargs, "output", Output)
+    validate_outputs = outputs
+    if len(outputs) == 1:
+        out0 = kwargs.get("output", args[0] if args else None)
+        if not isinstance(out0, (list, tuple)):
+            outputs = outputs[0]
+
+    inputs = extract_callback_args(flat_args, kwargs, "inputs", Input)
+    states = extract_callback_args(flat_args, kwargs, "state", State)
+
+    types = Input, Output, State
+    validate_callback(validate_outputs, inputs, states, flat_args, types)
+
+    return outputs, inputs, states, prevent_initial_call

package.json

@@ -5,7 +5,7 @@
     "private::format.black": "black dash tests --exclude metadata_test.py",
     "private::format.renderer": "cd dash-renderer && npm run format",
     "private::initialize.renderer": "cd dash-renderer && npm ci",
-    "private::lint.black": "if [[ $PYLINTRC != '.pylintrc' ]]; then black dash tests --exclude metadata_test.py --check; fi",
+    "private::lint.black": "if [ ${PYLINTRC:-x} != '.pylintrc' ]; then black dash tests --exclude metadata_test.py --check; fi",
     "private::lint.flake8": "flake8 --exclude=metadata_test.py dash tests",
     "private::lint.pylint-dash": "PYLINTRC=${PYLINTRC:=.pylintrc37} && pylint dash setup.py --rcfile=$PYLINTRC",
     "private::lint.pylint-tests": "PYLINTRC=${PYLINTRC:=.pylintrc37} && pylint tests/unit tests/integration -d all --rcfile=$PYLINTRC",

tests/assets/simple_app.py

@@ -18,7 +18,7 @@
 )
 
 
-@app.callback(Output("out", "children"), [Input("value", "value")])
+@app.callback(Output("out", "children"), Input("value", "value"))
 def on_value(value):
     if value is None:
         raise PreventUpdate

tests/integration/callbacks/test_basic_callback.py

@@ -342,3 +342,53 @@ def set_path(n):
     if not refresh:
         dash_duo.find_element("#btn").click()
         dash_duo.wait_for_text_to_equal("#out", '[{"a": "/2:a"}] - /2')
+
+
+def test_cbsc008_wildcard_prop_callbacks(dash_duo):
+    app = dash.Dash(__name__)
+    app.layout = html.Div(
+        [
+            dcc.Input(id="input", value="initial value"),
+            html.Div(
+                html.Div(
+                    [
+                        1.5,
+                        None,
+                        "string",
+                        html.Div(
+                            id="output-1",
+                            **{"data-cb": "initial value", "aria-cb": "initial value"}
+                        ),
+                    ]
+                )
+            ),
+        ]
+    )
+
+    input_call_count = Value("i", 0)
+
+    @app.callback(Output("output-1", "data-cb"), [Input("input", "value")])
+    def update_data(value):
+        input_call_count.value += 1
+        return value
+
+    @app.callback(Output("output-1", "children"), [Input("output-1", "data-cb")])
+    def update_text(data):
+        return data
+
+    dash_duo.start_server(app)
+    dash_duo.wait_for_text_to_equal("#output-1", "initial value")
+    dash_duo.percy_snapshot(name="wildcard-callback-1")
+
+    input1 = dash_duo.find_element("#input")
+    dash_duo.clear_input(input1)
+    input1.send_keys("hello world")
+
+    dash_duo.wait_for_text_to_equal("#output-1", "hello world")
+    dash_duo.percy_snapshot(name="wildcard-callback-2")
+
+    # an initial call, one for clearing the input
+    # and one for each hello world character
+    assert input_call_count.value == 2 + len("hello world")
+
+    assert not dash_duo.get_logs()