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Merged
merged 9 commits into from
Apr 8, 2019
Merged

Partial updates #680

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928d4b4
cleaner imports in test_integration
alexcjohnson Apr 4, 2019
fb0db30
simplify test Value usage
alexcjohnson Apr 4, 2019
b2a97b4
add no_update for partial or non-exception update rejection
alexcjohnson Apr 5, 2019
ba00dd7
test that no_update prevents chained callbacks
alexcjohnson Apr 8, 2019
681e8c5
robustify aborted callback test
alexcjohnson Apr 8, 2019
0ee047e
more test fixing - including @chriddyp's updates to wait_for_*
alexcjohnson Apr 8, 2019
ad42fa7
lint
alexcjohnson Apr 8, 2019
a0d17be
Merge branch 'master' into partial-update
alexcjohnson Apr 8, 2019
1689606
changelog for partial updates
alexcjohnson Apr 8, 2019
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
- Support for "Clientside Callbacks" - an escape hatch to execute your callbacks in JavaScript instead of Python [#672](https://github.com/plotly/dash/pull/672)
- Added `dev_tools_ui` config flag in `app.run_server` (serialized in `<script id="_dash-config" type="application/json">`)
to display or hide the forthcoming Dev Tools UI in Dash's front-end (dash-renderer). [#676](https://github.com/plotly/dash/pull/676)
- Partial updates: leave some multi-output updates unchanged while updating others [#680](https://github.com/plotly/dash/pull/680)

## [0.40.0] - 2019-03-25
### Changed
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2 changes: 1 addition & 1 deletion dash/__init__.py
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@@ -1,4 +1,4 @@
from .dash import Dash # noqa: F401
from .dash import Dash, no_update # noqa: F401
from . import dependencies # noqa: F401
from . import development # noqa: F401
from . import exceptions # noqa: F401
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23 changes: 21 additions & 2 deletions dash/dash.py
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Expand Up @@ -74,6 +74,15 @@
_re_renderer_scripts_id = re.compile(r'id="_dash-renderer')


class _NoUpdate(object):
# pylint: disable=too-few-public-methods
pass


# Singleton signal to not update an output, alternative to PreventUpdate
no_update = _NoUpdate()


# pylint: disable=too-many-instance-attributes
# pylint: disable=too-many-arguments, too-many-locals
class Dash(object):
Expand Down Expand Up @@ -1053,15 +1062,25 @@ def add_context(*args, **kwargs):
)

component_ids = collections.defaultdict(dict)
has_update = False
for i, o in enumerate(output):
component_ids[o.component_id][o.component_property] =\
output_value[i]
val = output_value[i]
if val is not no_update:
has_update = True
o_id, o_prop = o.component_id, o.component_property
component_ids[o_id][o_prop] = val
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Glad that we're returning a dict instead of a list here 😸 I was sure that we would've had to change the renderer to do this.


if not has_update:
raise exceptions.PreventUpdate
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Could use flask.abort instead of going the slow exception way.

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I don't know what flask.abort does, but I wanted to trigger the PreventDefault handler, in case the renderer does any optimizations with that specific response to maximize performance.

dash/dash/dash.py

Lines 180 to 183 in bb5ed70

@self.server.errorhandler(exceptions.PreventUpdate)
def _handle_error(_):
"""Handle a halted callback and return an empty 204 response"""
return '', 204

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It's an empty 204 which would be the same as flask.abort(204). Raising the exception takes longer because it has to be caught and then the handler is called whereas abort is immediate.

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Actually seems like flask.abort is doing more than that... if I try to do flask.abort(204) it fails with LookupError: no exception for 204. The docs say:

If a status code is given it’s looked up in the list of exceptions and will raise that exception

Which anyway sounds at least as complicated as what we're doing with raise PreventUpdate.

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Right, 204 is not an error. But then you are at the dispatch level, think you can just do return '', 204 and avoid any error handling.

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We're in the weeds now - the return from this function feeds into response.set_data() in the actual dispatch, which I don't believe accepts a status code.

dash/dash/dash.py

Line 1094 in b2a97b4

response.set_data(self.callback_map[output]['callback'](*args))

There may be a way to improve on this but I'd like to defer it for this PR, if that's alright.

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Ah, that's new. Anyway, this works well for partial updates.


response = {
'response': component_ids,
'multi': True
}
else:
if output_value is no_update:
raise exceptions.PreventUpdate

response = {
'response': {
'props': {
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22 changes: 15 additions & 7 deletions tests/IntegrationTests.py
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Expand Up @@ -21,15 +21,23 @@ def percy_snapshot(cls, name=''):
name=snapshot_name
)

def wait_for_element_by_css_selector(self, selector):
return WebDriverWait(self.driver, TIMEOUT).until(
EC.presence_of_element_located((By.CSS_SELECTOR, selector))
def wait_for_element_by_css_selector(self, selector, timeout=TIMEOUT):
return WebDriverWait(self.driver, timeout).until(
EC.presence_of_element_located((By.CSS_SELECTOR, selector)),
'Could not find element with selector "{}"'.format(selector)
)

def wait_for_text_to_equal(self, selector, assertion_text):
return WebDriverWait(self.driver, TIMEOUT).until(
EC.text_to_be_present_in_element((By.CSS_SELECTOR, selector),
assertion_text)
def wait_for_text_to_equal(self, selector, assertion_text, timeout=TIMEOUT):
el = self.wait_for_element_by_css_selector(selector)
WebDriverWait(self.driver, timeout).until(
lambda *args: (
(str(el.text) == assertion_text) or
(str(el.get_attribute('value')) == assertion_text)
),
"Element '{}' text was supposed to equal '{}' but it didn't".format(
selector,
assertion_text
)
)

@classmethod
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