Backport override features from edx-toggles to waffle_utils
Note that those features are destined to be deprecated, eventually.
This commit is contained in:
Régis Behmo
@@ -1,186 +1,110 @@
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"""
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Utilities for waffle.
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Extra utilities for waffle: most classes are defined in edx_toggles.toggles, but we keep here some extra classes for
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usage within edx-platform. These classes cover course override use cases.
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Includes namespacing, caching, and course overrides for waffle flags.
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Usage:
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For Waffle Flags, first set up the namespace, and then create flags using the
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namespace. For example::
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WAFFLE_FLAG_NAMESPACE = WaffleFlagNamespace(name='my_namespace')
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# Use CourseWaffleFlag when you are in the context of a course.
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SOME_COURSE_FLAG = CourseWaffleFlag(WAFFLE_FLAG_NAMESPACE, 'some_course_feature', __name__)
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# Use WaffleFlag when outside the context of a course.
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SOME_FLAG = WaffleFlag(WAFFLE_FLAG_NAMESPACE, 'some_feature', __name__)
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You can check these flags in code using the following::
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You can check this flag in code using the following::
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SOME_FLAG.is_enabled()
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SOME_COURSE_FLAG.is_enabled(course_key)
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To test these WaffleFlags, see testutils.py.
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In the above examples, you will use Django Admin "waffle" section to configure
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for a flag named: my_namespace.some_course_feature
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You could also use the Django Admin "waffle_utils" section to configure a course
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override for this same flag (e.g. my_namespace.some_course_feature).
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For Waffle Switches, first set up the namespace, and then create the flag name.
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For example::
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WAFFLE_SWITCHES = WaffleSwitchNamespace(name=WAFFLE_NAMESPACE)
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ESTIMATE_FIRST_ATTEMPTED = 'estimate_first_attempted'
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You can then use the switch as follows::
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WAFFLE_SWITCHES.is_enabled(waffle.ESTIMATE_FIRST_ATTEMPTED)
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To test WaffleSwitchNamespace, use the provided context managers. For example:
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with WAFFLE_SWITCHES.override(waffle.ESTIMATE_FIRST_ATTEMPTED, active=True):
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...
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For long-lived flags, you may want to change the default for devstack, sandboxes,
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or new Open edX releases. For help with this, see:
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openedx/core/djangoapps/waffle_utils/docs/decisions/0001-refactor-waffle-flag-default.rst
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Also see ``WAFFLE_FLAG_CUSTOM_ATTRIBUTES`` and docstring for _set_waffle_flag_attribute
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for temporarily instrumenting/monitoring waffle flag usage.
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"""
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from functools import lru_cache
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import logging
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from contextlib import contextmanager
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from weakref import WeakSet
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from django.conf import settings
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from edx_django_utils.monitoring import set_custom_attribute
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from opaque_keys.edx.keys import CourseKey
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from edx_toggles.toggles import WaffleFlag as BaseWaffleFlag
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from edx_toggles.toggles import WaffleFlagNamespace as BaseWaffleFlagNamespace
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from edx_toggles.toggles import WaffleFlagNamespace
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from edx_toggles.toggles import WaffleSwitch as BaseWaffleSwitch
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from edx_toggles.toggles import WaffleSwitchNamespace as BaseWaffleSwitchNamespace
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from openedx.core.lib.cache_utils import get_cache as get_request_cache
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log = logging.getLogger(__name__)
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class WaffleSwitchNamespace(BaseWaffleSwitchNamespace):
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"""
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A waffle switch namespace class that implements request-based caching.
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Waffle switch namespace that implements custom overriding methods. We should eventually get rid of this class.
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"""
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@property
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def _cached_switches(self):
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@contextmanager
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def override(self, switch_name, active=True):
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"""
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Returns a dictionary of all namespaced switches in the request cache.
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Overrides the active value for the given switch for the duration of this
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contextmanager.
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Note: The value is overridden in the request cache AND in the model.
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"""
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return _get_waffle_namespace_request_cache().setdefault("switches", {})
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previous_active = self.is_enabled(switch_name)
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try:
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self.override_for_request(switch_name, active)
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with self.override_in_model(switch_name, active):
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yield
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finally:
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self.override_for_request(switch_name, previous_active)
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def override_for_request(self, switch_name, active=True):
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"""
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Overrides the active value for the given switch for the remainder of
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this request (as this is not a context manager).
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Note: The value is overridden in the request cache, not in the model.
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"""
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namespaced_switch_name = self._namespaced_name(switch_name)
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self._cached_switches[namespaced_switch_name] = active
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log.info(
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"%sSwitch '%s' set to %s for request.",
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self.log_prefix,
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namespaced_switch_name,
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active,
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)
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def _get_waffle_namespace_request_cache():
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"""
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Returns a request cache shared by all Waffle namespace objects.
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"""
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return get_request_cache("WaffleNamespace")
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@contextmanager
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def override_in_model(self, switch_name, active=True):
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"""
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Overrides the active value for the given switch for the duration of this
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contextmanager.
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Note: The value is overridden in the model, not the request cache.
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Note: This should probably be moved to a test class.
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"""
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# Import is placed here to avoid model import at project startup.
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# pylint: disable=import-outside-toplevel
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from waffle.testutils import override_switch as waffle_override_switch
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namespaced_switch_name = self._namespaced_name(switch_name)
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with waffle_override_switch(namespaced_switch_name, active):
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log.info(
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"%sSwitch '%s' set to %s in model.",
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self.log_prefix,
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namespaced_switch_name,
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active,
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)
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yield
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class WaffleSwitch(BaseWaffleSwitch):
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"""
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Waffle switch class that benefits from the additional features of the WaffleSwitchNamespace.
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This class should be removed in favour of edx_toggles.toggles.WaffleSwitch once we get rid of the
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WaffleSwitchNamespace class.
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"""
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NAMESPACE_CLASS = WaffleSwitchNamespace
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class WaffleFlagNamespace(BaseWaffleFlagNamespace):
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"""
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Namespace class that implements request-based caching. Also, setup some custom value-checking and processing.
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"""
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@property
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def _cached_flags(self):
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"""
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Returns a dictionary of all namespaced flags in the request cache.
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"""
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return _get_waffle_namespace_request_cache().setdefault("flags", {})
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def _get_flag_active(self, namespaced_flag_name):
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value = super()._get_flag_active(namespaced_flag_name)
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_set_waffle_flag_attribute(namespaced_flag_name, value)
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return value
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def _get_flag_active_default(self, namespaced_flag_name):
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value = super()._get_flag_active_default(namespaced_flag_name)
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set_custom_attribute("warn_flag_no_request_return_value", value)
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return value
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# .. toggle_name: WAFFLE_FLAG_CUSTOM_ATTRIBUTES
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# .. toggle_implementation: DjangoSetting
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# .. toggle_default: False
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# .. toggle_description: A list of waffle flags to track with custom attributes having
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# values of (True, False, or Both).
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# .. toggle_use_cases: opt_in
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# .. toggle_creation_date: 2020-06-17
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# .. toggle_warnings: Intent is for temporary research (1 day - several weeks) of a flag's usage.
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@lru_cache(maxsize=None)
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def _get_waffle_flag_custom_attributes_set():
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attributes = getattr(settings, "WAFFLE_FLAG_CUSTOM_ATTRIBUTES", None) or []
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return set(attributes)
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def _set_waffle_flag_attribute(name, value):
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"""
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For any flag name in settings.WAFFLE_FLAG_CUSTOM_ATTRIBUTES, add name/value
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to cached values and set custom attribute if the value changed.
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The name of the custom attribute will have the prefix ``flag_`` and the
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suffix will match the name of the flag.
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The value of the custom attribute could be False, True, or Both.
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The value Both would mean that the flag had both a True and False
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value at different times during the transaction. This is most
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likely due to having a course override, as is the case with
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CourseWaffleFlag.
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An example NewRelic query to see the values of a flag in different
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environments, if your waffle flag was named ``my.waffle.flag`` might
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look like::
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SELECT count(*) FROM Transaction
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WHERE flag_my.waffle.flag IS NOT NULL
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FACET appName, flag_my.waffle.flag
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Important: Remember to configure ``WAFFLE_FLAG_CUSTOM_ATTRIBUTES`` for
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LMS, Studio and Workers in order to see waffle flag usage in all
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edx-platform environments.
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"""
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if name not in _get_waffle_flag_custom_attributes_set():
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return
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flag_attribute_data = _get_waffle_namespace_request_cache().setdefault(
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"flag_attribute", {}
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)
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is_value_changed = True
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if name not in flag_attribute_data:
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# New flag
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flag_attribute_data[name] = str(value)
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else:
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# Existing flag
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if flag_attribute_data[name] == str(value):
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# Same value
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is_value_changed = False
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else:
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# New value
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flag_attribute_data[name] = "Both"
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if is_value_changed:
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attribute_name = "flag_{}".format(name)
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set_custom_attribute(attribute_name, flag_attribute_data[name])
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@contextmanager
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def override(self, active=True):
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with self.waffle_namespace.override(self.switch_name, active):
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yield
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class WaffleFlag(BaseWaffleFlag):
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@@ -190,7 +114,6 @@ class WaffleFlag(BaseWaffleFlag):
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This class should be removed in favour of edx_toggles.toggles.WaffleFlag once we get rid of the WaffleFlagNamespace
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class and the `override` method.
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"""
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NAMESPACE_CLASS = WaffleFlagNamespace
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@contextmanager
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def override(self, active=True):
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@@ -271,6 +194,9 @@ class CourseWaffleFlag(WaffleFlag):
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)
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is_enabled_for_course = self._get_course_override_value(course_key)
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if is_enabled_for_course is not None:
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_set_waffle_flag_attribute(self.namespaced_flag_name, is_enabled_for_course)
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# pylint: disable=protected-access
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self.namespace._monitor_value(
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self.namespaced_flag_name, is_enabled_for_course
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)
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return is_enabled_for_course
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return super().is_enabled()
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