Topics

diffusion.features.topics.Topics

Bases: Component

Topics component.

It is not supposed to be instantiated independently; an instance is available on each Session instance as session.topics.

topics property

topics: dict

Internal storage for registered topics.

add_topic async

add_topic(topic_path: str, specification: DataTypeArgument) -> TopicAddResponse

Create a new topic of the given type and properties.

Parameters:

Name	Type	Description	Default
topic_path	str	The path to create the topic on.	required
specification	DataTypeArgument	Data type of the topic.	required

add_and_set_topic async

add_and_set_topic(topic_path: str, specification: DataTypeArgument, value: Any, constraint: UpdateConstraint = None) -> TopicAddResponse

Create a new topic of the given type and properties.

Parameters:

Name	Type	Description	Default
topic_path	str	The path to create the topic on.	required
specification	DataTypeArgument	Data type of the topic.	required
value	Any	Value to set when creating the topic. The value needs to be compatible with the topic_type. If the topic already exists, this will be set as its value.	required
constraint	UpdateConstraint	optional update constraint	None

set_topic async

set_topic(topic_path: str, value: Any, specification: DataTypeArgument, constraint: UpdateConstraint = None) -> None

Sets the topic to a specified value.

None can only be passed to the value parameter when updating STRING, INT64, or DOUBLE topics.

When a STRING, INT64, or DOUBLE topic is set to None, the topic will be updated to have no value. If a previous value was present subscribers will receive a notification that the new value is None. New subscribers will not receive a value notification.

Parameters:

Name	Type	Description	Default
topic_path	str	the path of the topic	required
specification	DataTypeArgument	Data type of the topic.	required
value	Any	the value. STRING, INT64, or DOUBLE topics accept None, as described above. Using None with other topic types is an error and will throw an UnknownDataTypeError.	required
constraint	UpdateConstraint	optional update constraint	None

remove_topic async

remove_topic(topic_selector: str) -> TopicRemovalResult

Remove all the topics that match the given selector.

Parameters:

Name	Type	Description	Default
topic_selector	str	The topics matching this selector will be removed from the server.	required

Returns:

Type	Description
TopicRemovalResult	An object detailing the results.

add_value_stream

add_value_stream(topic_selector: str, stream: ValueStreamHandler) -> None

Registers a value stream handler for a topic selector.

A value stream is a series of events associated with a registered topic. This method adds a ValueStreamHandler which can handle those events.

Parameters:

Name	Type	Description	Default
topic_selector	str	The handler will react to the updates to all topics matching this selector.	required
stream	ValueStreamHandler	A handler for incoming events of the matching data type.	required

add_fallback_stream

add_fallback_stream(stream: ValueStreamHandler) -> None

Registers a fallback stream handler for a topic type.

A value stream is a series of events associated with a registered topic. This method makes it possible to register callbacks for each of those events.

Parameters:

Name	Type	Description	Default
stream	ValueStreamHandler	A handler for the matching data type.	required

subscribe async

subscribe(topic_selector: str)

Register the session to receive updates for the given topic.

Parameters:

Name	Type	Description	Default
topic_selector	str	The selector for topics to subscribe to.	required

unsubscribe async

unsubscribe(topic_selector: str)

Unregister the session to stop receiving updates for the given topic.

Parameters:

Name	Type	Description	Default
topic_selector	str	The selector for topics to unsubscribe from.	required

diffusion.features.topics.details.topic_specification

T_other module-attribute

T_other = typing.TypeVar('T_other', bound=DataType)

A DataType type variable.

WithProperties

Bases: typing.Generic[T]

CompressionPolicy

Bases: str, enum.Enum

Compression Level

OFF class-attribute instance-attribute

OFF = 'off'

Disables compression completely for the topic and requires no additional CPU.

LOW class-attribute instance-attribute

LOW = 'low'

Low compression.

Generally some compression is beneficial, so the default value for this property is this.

MEDIUM class-attribute instance-attribute

MEDIUM = 'medium'

Medium compression.

HIGH class-attribute instance-attribute

HIGH = 'high'

Compresses the topic messages to the smallest number of bytes, but has the highest CPU cost.

TopicDeliveryPriority

Bases: str, enum.Enum

Topic Delivery Priority

LOW class-attribute instance-attribute

LOW = 'low'

Low priority.

DEFAULT class-attribute instance-attribute

DEFAULT = 'default'

Default priority.

HIGH class-attribute instance-attribute

HIGH = 'high'

High priority.

ConflationPolicy

Bases: str, enum.Enum

Conflation Policy

OFF class-attribute instance-attribute

OFF = 'off'

Disables conflation for the topic. This policy disables all conflation for the topic, so topic updates will never be merged or discarded.

CONFLATE class-attribute instance-attribute

CONFLATE = 'conflate'

Automatically conflates topic updates when back pressure is detected by the server.

UNSUBSCRIBE class-attribute instance-attribute

UNSUBSCRIBE = 'unsubscribe'

Automatically unsubscribes the topic when back pressure is detected by the server. The unsubscription is not persisted to the cluster. If a session fails over to a different server it will be resubscribed to the topic.

ALWAYS class-attribute instance-attribute

ALWAYS = 'always'

Automatically conflates topic updates as they are queued for the session. This is an eager policy that ensures only the latest update is queued for the topic, minimising the server memory and network bandwidth used by the session.

TopicSpecification

Bases: typing.Generic[T], pydantic.generics.GenericModel

Topic specifications provide the information required to create a topic. Topics can be created from a topic specification using add_topic.

Topic specifications allow an application to introspect the type and capabilities of a topic. Topic specifications are provided to ValueStream value streams and TopicNotifications topic notification listeners

A topic specification has a topic type and a map of property settings which define the behavior of the topic. A

Topic specification types can be derived from any datatype using its with_properties member. This will return a TopicSpecification type ready for instantiation with the relevant parameters.

Topic specifications with different properties can be derived from any instance using with_properties.

Topic Properties

Depending on the topic type, some properties must be included in the specification when creating a topic and some properties have no effect. The required and optional properties for each the topic type are set out in the following table. Properties unsupported by the topic type are ignored.

Default when optional	STRING JSON BINARY	DOUBLE INT64	RECORD_V2	TIME_SERIES
COMPRESSION	CompressionPolicy.LOW	Optional	—	Optional
CONFLATION	ConflationPolicy.CONFLATE	Optional	Optional	Optional
DONT_RETAIN_VALUE	False	Optional	Optional	Optional
OWNER	Optional	Optional	Optional	Optional
PERSISTENT	True	Optional	Optional	Optional
PRIORITY	TopicDeliveryPriority.DEFAULT	Optional	Optional	Optional
PUBLISH_VALUES_ONLY	False	Optional	—	Optional
REMOVAL	Optional	Optional	Optional	Optional
SCHEMA	—	—	Optional	—
TIDY_ON_UNSUBSCRIBE	False	Optional	Optional	Optional
TIME_SERIES_EVENT_VALUE_TYPE	—	—	—	Required
TIME_SERIES_RETAINED_RANGE	limit 10	—	—	—
TIME_SERIES_SUBSCRIPTION_RANGE	TIME_SERIES_SUBSCRIPTION_RANGE As documented
VALIDATE_VALUES	False	Optional	Optional	Optional

† TIME_SERIES topics have restricted values for the CONFLATION property. They are only allowed to have the values OFF or UNSUBSCRIBE.

topic_type property

topic_type: typing.Type[T]

The topic datatype.

Returns:

Type	Description
typing.Type[T]	The topic datatype.

with_properties class-attribute instance-attribute

with_properties: typing.ClassVar[WithProperties] = WithProperties()

Class property providing a TopicSpecification subtype ready for instantiation.

PUBLISH_VALUES_ONLY class-attribute instance-attribute

PUBLISH_VALUES_ONLY: typing.Optional[bool] = None

Key of the topic property that specifies whether a topic should publish only values.

By default, a topic that supports delta streams will publish the difference between two values (a delta) when doing so is more efficient than publishing the complete new value. Subscribing sessions can use a ValueStream value stream to automatically apply the delta to a local copy of the topic value to calculate the new value.

Setting PUBLISH_VALUES_ONLY to True disables this behavior so that deltas are never published. Doing so is usually not recommended because it will result in more data being transmitted, less efficient use of network resources, and increased transmission latency. On the other hand, calculating deltas can require significant CPU from the server or, if update streams are used, from the updating client. The CPU cost will be higher if there are many differences between successive values, in which case delta streams confer fewer benefits. If successive values are unrelated to each other, consider setting PUBLISH_VALUES_ONLY to True. Also consider setting PUBLISH_VALUES_ONLY to True if the network capacity is high and the bandwidth savings of deltas are not required.

See also: DONT_RETAIN_VALUE

VALIDATE_VALUES class-attribute instance-attribute

VALIDATE_VALUES: typing.Optional[bool] = None

Key of the topic property indicating whether a topic should validate inbound values.

By default, the server does not validate received values before sending them on to client sessions. Invalid or corrupt values will be stored in the topic and passed on to sessions. If this property is set to True, the server will perform additional validation on values to check that they are valid instances of the data type, and if it is not then it will return an error to the updater and not update the topic.

If this value is not set (or set to something other than True), no server validation of inbound values is performed. This is the recommended setting as there is a performance overhead to validation and a session using Topic Update cannot send invalid values anyway.

TIDY_ON_UNSUBSCRIBE class-attribute instance-attribute

TIDY_ON_UNSUBSCRIBE: typing.Optional[bool] = None

Key of the topic property that specifies the 'tidy on unsubscribe' option for a topic.

By default, if a session unsubscribes from a topic, it will receive any updates for that topic that were previously queued but not sent.

If this property is set to "True", when a session unsubscribes from the topic, any updates for the topic that are still queued for the session are removed. There is a performance overhead to using this option as the client queue must be scanned to find topic updates to remove, however it may prove useful for preventing unwanted data being sent to sessions.

Since 6.8.3

SCHEMA class-attribute instance-attribute

SCHEMA: typing.Optional[str] = None

Key of the topic property that specifies a schema which constrains topic values.

This property is only used by RECORD_V2 topics.

Since 6.8.3

DONT_RETAIN_VALUE class-attribute instance-attribute

DONT_RETAIN_VALUE: typing.Optional[bool] = None

Key of the topic property that specifies a topic should not retain its last value.

By default, a topic will retain its latest value. The latest value will be sent to new subscribers. Setting this property to True disables this behavior. New subscribers will not be sent an initial value. No value will be returned for fetch operations that select the topic. This is useful for data streams where the values are only transiently valid.

Setting DONT_RETAIN_VALUE to True also disables delta streams, regardless of the PUBLISH_VALUES_ONLY value. If subsequent values are likely to be related, delta streams usually provide performance benefits (see PUBLISH_VALUES_ONLY). Consider leaving DONT_RETAIN_VALUE set to False to benefit from delta streams, even if there is no other requirement to retain the last value.

Bearing in mind the performance trade-offs of disabling delta streams, there are two reasons to consider setting DONT_RETAIN_VALUE to True. First, it stops the server and each subscribed client from keeping a copy of the value, reducing their memory requirements. Second, when a topic has a high update rate and is replicated across a cluster, it can significantly improve throughput because the values need not be persisted to the cluster.

Time series topics ignore this property and always retain the latest value.

Since 6.8.3

PERSISTENT class-attribute instance-attribute

PERSISTENT: typing.Optional[bool] = None

Key of the topic property that can be used to prevent a topic from being persisted when the server is configured to enable persistence.

By default, a topic will be persisted if persistence is enabled at the server and the topic type supports persistence. Setting PERSISTENT to `false` will prevent the topic from being persisted. Since 6.8.3

REMOVAL class-attribute instance-attribute

REMOVAL: typing.Optional[str] = None

Key of the topic property that specifies a removal policy for automatic removal of the topic (and/or other topics). This property is specified as an expression which defines one or more conditions that are to be satisfied before automatic removal occurs. The expression takes the form: when conditions [remove "selector"] At least one condition must be supplied. If more than one is supplied, they must be separated by logical operators (and or or). The natural evaluation order of the operators may be changed by surrounding with parentheses (e.g. (condition and condition)). The remove clause is optional. It provides a Topic Selector expression representing the topics to be removed. If a remove clause is specified, the topic with the removal policy will only be removed if its path matches the selector expression. The selector must be surrounded by either double or single quotes. When many topics have the same removal policy, it is better to set the REMOVAL property for one of them, using a remove clause that selects all of the topics. This is more efficient because it allows the server to avoid evaluating the same condition many times.

The permissions that are applied at the time of removal are those defined by the roles of the principal that created the topic at the time of creation. The roles of that principal may therefore change before the removal with no effect, but if the permissions given to the roles change it may have an effect upon the final removal. Only one occurrence of each of the following condition types may be included within the expression:

Condition Type	Format	Usage
time after	time after absoluteTime	Removal should occur after a specified absolute time. Absolute time may be specified as a number of milliseconds since the epoch (00:00:00 on 1 January 1970) or as a quoted date and time formatted in RFC_1123 date time format. Either single or double quotes may be used.
subscriptions less than	[local] subscriptions < n for  forPeriod [after afterPeriod]	Removal should occur when the topic has had less than the specified number (n) of subscriptions for a given period (forPeriod) of time. Optionally, an initial period (afterPeriod) may be specified by which to delay the initial checking of this condition. See below for period formats. The optional local keyword restricts evaluation to only count subscriptions from sessions belonging to the local server or cluster, ignoring subscriptions from sessions belonging to downstream remote servers that host fanout replicas of the topic.
no updates for	no updates for forPeriod [after afterPeriod]	Removal should occur when the topic has had no updates for a given period (forPeriod) of time. Optionally, an initial period (afterPeriod) may be specified by which to delay the initial checking of this condition. See below for period formats.

Multiple occurrences of the following condition types may be included within the expression:

Condition Type	Format	Usage
no session has	no [local] session has "criteria" [for forPeriod] [after afterPeriod]	Removal should occur when there are no sessions satisfying certain criteria. Optionally the criteria can be required to be satisfied for a period of time (forPeriod). Optionally, an initial period (afterPeriod) can be specified to delay the initial check of the criteria. Session selection criteria are specified as defined in session filters and must be surrounded by single or double quotes. See below for period formats. The optional local keyword restricts evaluation to sessions belonging to the local server or cluster, ignoring sessions belonging to downstream remote servers that host fanout replicas of the topic.
this session closes	This is a shorthand form of no local session has that may be used to indicate that the topic is to be removed when the session that created it closes.

Time periods are specified as a number followed (with no intermediate space) by a single letter representing the time unit. The time unit may be s (seconds), m (minutes), h (hours) or d (days). For example, 10 minutes would be specified as 10m. If quotes or backslashes \ are required within quoted values such as selectors or session criteria then they may be escaped by preceding with \. The expression is validated only by the server and therefore if an invalid expression is specified it will be reported as an InvalidTopicSpecificationError.

** Examples: **

when time after 1518780068112

The topic will be removed when the date and time indicated by the specified number of milliseconds since the epoch has passed.

when time after "Tue, 3 Jun 2018 11:05:30 GMT"

The topic will be removed when the specified date and time has passed.

when time after "Tue, 3 Jun 2018 11:05:30 GMT" remove "*alpha/beta//"

The topic alpha/beta and all topics subordinate to it will be removed when the specified date and time has passed.

when subscriptions < 1 for 20m

The topic will be removed when it has had no subscriptions for a continuous period of 20 minutes.

when subscriptions < 2 for 20m after 1h

The topic will be removed when it has had less than 2 subscriptions for a continuous period of 20 minutes after one hour has passed since its creation.

when no updates for 3h

The topic will be removed when it has had no updates for a continuous period of 3 hours.

when no updates for 15m after 1d

The topic will be removed when it has had no updates for a continuous period of 15 minutes after one day has passed since its creation.

when this session closes

The topic will be removed when the session creating it closes.

when no session has '$Principal is "Alice"'

The topic will be removed when there are no sessions with the principal 'Alice'.

when no session has '$Principal is "Alice"' for 10m

The topic will be removed when there are no sessions with the principal 'Alice' for a continuous period of 10 minutes.

when no session has 'Department is "Accounts"' for 30m after 2h

The topic will be removed when there have been no sessions from the Accounts department for a continuous period of 30 minutes after 2 hours have passed since its creation.

when time after "Tue, 3 Jun 2018 11:05:30 GMT" and subscriptions < 1 for 30m

The topic will be removed when the specified date and time has passed and the topic has had no subscriptions for a continuous period of 30 minutes after that time.

when time after "Tue, 3 Jun 2018 11:05:30 GMT" and subscriptions < 2 for 10m after 1h

The topic will be removed when the specified date and time has passed and the topic has had less than 2 subscriptions for a continuous period of 10 minutes after that time plus one hour.

when time after "Tue, 3 Jun 2018 11:05:30 GMT" or subscriptions < 2 for 10m after 1h

The topic will be removed when the specified date and time has passed or the topic has had less than 2 subscriptions for a continuous period of 10 minutes after one hour from its creation.

when time after "Tue, 3 Jun 2018 11:05:30 GMT" and (subscriptions < 2 for 10m after 1h or no updates for 20m)

The topic will be removed when the specified date and time has passed and either the topic has had less than 2 subscriptions for a continuous period of 10 minutes after that time plus one hour or it has had no updates for a continuous period of 20 minutes. Note that the parentheses are significant here as without them the topic would be removed if it had had no updates for 20 minutes regardless of the time and subscriptions clause.

Notes and restrictions on use

The after time periods refer to the period since the topic was created or restored from persistence store after a server is restarted. They are designed as a 'grace' period after the topic comes into existence before the related condition starts to be evaluated. When not specified the conditions start to be evaluated as soon as the topic is created or restored. The server will evaluate conditions on a periodic basis (every few seconds) so the exact removal time will not be precise for low periodic granularity. The meaning of the for period in a no session has condition is subtly different from its use in other conditions. It does not guarantee that there has been no session satisfying the condition at some point between evaluations, only that when evaluated the given period of time has passed since it was last evaluated and found to have no matching sessions. Subscriptions is the number of subscriptions to a topic. Automatic topic removal is supported for a topic that is replicated across the local cluster, and for a topic with with fanout replicas on downstream remote servers. A subscriptions less than condition will be evaluated against the total number of subscriptions across the cluster and on all fanout replicas on downstream remote servers. A no session has condition will consider all sessions hosted across the cluster and all sessions hosted by downstream remote servers that have a fanout replica of the topic. The local keyword can be used to restrict evaluation to the local cluster, ignoring fanout replicas.

Since 6.8.3

CONFLATION class-attribute instance-attribute

CONFLATION: typing.Optional[ConflationPolicy] = None

The conflation policy of the topic. The policy specifies how the server manages queued topic updates. Conflation is applied individually to each session queue. Conflation is the process of merging or discarding topic updates queued for a session to reduce the server memory footprint and network data. The server will conflate sessions that have a large number of queued messages to meet configured queue size targets. The sessions with the largest queues are typically slow consumers or have been disconnected – both will benefit from conflation. This property allows conflation behavior to be tuned on a topic-by-topic basis.

The supported policies are:

• OFF
• CONFLATE
• UNSUBSCRIBE
• ALWAYS

The default policy used when the property is not specified and the topic type is not time series is CONFLATE. The default policy used when the property is not specified and the topic type is time series is OFF.

See ConflationPolicy for more.

The CONFLATE and UNSUBSCRIBE policies are applied when the server detects back pressure for a session. The server configuration places limits on the data queued for each session. If these limits are breached, the server will conflate the session queue to attempt to reducee its size. If the session queue still exceeds the limits after conflation, the session will be terminated. Conflation can be disabled on a session-by-session basis. If conflation is disabled for a session the policy will not be applied to topic updates queued for the session but will be for other sessions that have conflation enabled. The policies CONFLATE and ALWAYS are not supported for time series topics as they would cause missing events. Attempts to enable these policies with time series topics will cause the creation of the topic to fail, reporting that the specification is invalid.

Since 6.8.3

OWNER class-attribute instance-attribute

OWNER: typing.Optional[str] = None

Key of the topic property that allows the creator of a topic to extend READ_TOPIC, MODIFY_TOPIC, and UPDATE_TOPIC permissions to a specific principal, in addition to the permissions granted by the authorisation rules in the security store. A session that has authenticated using the principal can update and remove the topic, so the principal can be considered the topic owner. To fetch or subscribe to the topic, the principal must also be granted the SELECT_TOPIC permission by the security store rules. This may be used in the following cases:
1) A session creates a topic and makes its own principal the owner.
2) A session creates a topic and makes another principal the owner. The format of the property value is: $Principal is name where name is the name of the principal. Single quotes may be used instead of double quotes and special characters can be escaped. The purpose of this property is to allow a client to create topics on behalf of other users. This can be used in conjunction with the REMOVAL property so that such topics are removed when there are no longer any sessions for the named principal. For example:

>>> import diffusion.datatypes
>>> specification = diffusion.datatypes.JSON
>>> specification.with_properties(OWNER="$Principal is 'myPrincipal'", REMOVAL="when no session has '$Principal is "myPrincipal"' for 5s")

Since 6.8.3

COMPRESSION class-attribute instance-attribute

COMPRESSION: typing.Optional[typing.Union[CompressionPolicy, bool]] = None

Key of the topic property that allows the compression policy to be set on a per-topic basis.

Compression reduces the bandwidth required to broadcast topic updates to subscribed sessions, at the cost of increased server CPU.

Changes to a topic's value are published to each subscribed session as a sequence of topic messages. A topic message can carry the latest value or the difference between the latest value and the previous value (a delta). The compression policy determines if and how published topic messages are compressed. Topic messages are not exposed through the client API; the client library handles decompression and decodes deltas automatically, passing reconstructed values to the application.

The compression policy for a topic is specified by setting this property to one of several values:

• OFF
• LOW
• MEDIUM
• HIGH

The policies are listed in the order of increasing compression and increasing CPU cost.

See Also

CompressionPolicy

Prior to version 6.4, only two values were allowed: True (equivalent to MEDIUM, and the previous default policy) and False (equivalent to OFF). These values are still supported.

This property is only one factor that determines whether a topic message will be compressed. Other factors include:

• Compression must be enabled in the server configuration.
• The client library must support the server's compression scheme. In this release, the server supports zlib compression, and also allows compression to be disabled on a per-connector basis. From 6.4, all client libraries are capable of zlib compression. A JavaScript client may or may not support zlib compression, depending on whether the zlib library can be loaded. The zlib library is packaged separately to reduce the download size of the core library.

Since 6.8.3

PRIORITY class-attribute instance-attribute

PRIORITY: typing.Optional[TopicDeliveryPriority] = None

Key of the topic property that specifies the topic delivery priority. The supported delivery priorities are:

• LOW
• DEFAULT
• HIGH

The delivery priority affects the order of topic updates sent to a subscribed client session. When there are multiple topic updates for topics with different priorities in a session's outbound queue, updates for HIGH priority topics will be delivered first, followed by updates for DEFAULT priority topics, followed by updates for LOW priority topics. Topic subscription and unsubscription notifications are also delivered according to the topic delivery priority.

Using different delivery priorities is most beneficial when there is a large backlog of queued updates to deliver to a client session. On lightly loaded systems, updates typically remain in the outbound queue for a few milliseconds and so there is a lower chance of topic updates being reordered based on their priority. The backlog will be larger if the topic update rate is higher; the server or the client are more heavily loaded; the client session becomes temporarily disconnected; or if there is poor network connectivity between the server and the client.

Messages from the server to the client that are not topic updates, for example ping requests and responses, are queued with the DEFAULT delivery priority.

Since 6.8.3

new_topic_specification classmethod

new_topic_specification(tp: typing.Type[T_other]) -> typing.Type[TopicSpecification[T_other]]

Return a TopicSpecification class with datatype tp, ready for instantiation.

This is for internal use - to get a TopicSpecification for a given DataType you should use its with_properties member, which will return an appropriate TopicSpecification type ready for instantiation with the relevant parameters.

Parameters:

Name	Type	Description	Default
tp	typing.Type[T_other]	the datatype	required

Returns:

Type	Description
typing.Type[TopicSpecification[T_other]]	A new TopicSpecification with the given type

diffusion.features.topics.streams

Stream handlers for topics.

ValueStreamHandler

Bases: EventStreamHandler

Stream handler implementation for the value streams of the given type.

diffusion.features.topics.selectors

Matching of topic selectors.

Selector

Bases: Protocol, Hashable

Generic protocol for all selectors.

raw property

raw: str

The original, unoptimised value of the selector.

match

match(topic_path: str) -> bool

Compares a topic path against the selector.

Parameters:

Name	Type	Description	Default
topic_path	str	The topic path to match against the selector.	required

Returns:

Type	Description
bool	True if the path matches the selector; False otherwise.

TopicSelectorError

Bases: DiffusionError

Error related to selector matching.

PathSelector

Bases: Selector

Basic topic selector, matching the topic path exactly.

Parameters:

Name	Type	Description	Default
selector	str	The topic selector text.	required

raw property

raw: str

The original, unoptimised value of the selector.

match

match(topic_path: str) -> bool

Compares a topic path against the selector.

Parameters:

Name	Type	Description	Default
topic_path	str	The topic path to match against the selector.	required

Returns:

Type	Description
bool	True if the path matches the selector; False otherwise.

PatternSelector

Bases: PathSelector

Common functionality of pattern selectors.

FullPathPatternSelector

Bases: PatternSelector

Selector containing a regular expression matching the entire path.

A full-path pattern topic selector returns topics for which the regular expression matches the full topic path.

Parameters:

Name	Type	Description	Default
selector	str	The topic selector text.	required

match

match(topic_path: str) -> bool

Compares a topic path against the selector.

Parameters:

Name	Type	Description	Default
topic_path	str	The topic path to match against the selector.	required

Returns:

Type	Description
bool	True if the path matches the selector; False otherwise.

SplitPathPatternSelector

Bases: PatternSelector

Selector containing split-path regular expression pattern.

A split-path pattern expression contains a list of regular expressions separated by the / character. Each regular expression describes a part of the topic path. The selector returns topics for which each regular expression matches the part of the topic path at the corresponding level.

Parameters:

Name	Type	Description	Default
selector	str	The topic selector text.	required

match

match(topic_path: str) -> bool

Compares a topic path against the selector.

Parameters:

Name	Type	Description	Default
topic_path	str	The topic path to match against the selector.	required

Returns:

Type	Description
bool	True if the path matches the selector; False otherwise.

SelectorSet

Bases: Set[Selector], Selector

A set of multiple path or pattern selectors.

A selector set returns topics that match any of the selectors. Its textual form is a list of selectors separated by the separator ////.

Parameters:

Name	Type	Description	Default
selectors	Union[str, Iterable[str]]	Either the full list of selectors (separated by ////) or an iterable of individual selectors.	required

raw property

raw: str

The original, unoptimised value of the selector.

match

match(topic_path: str) -> bool

Compares a topic path against the selector.

Parameters:

Name	Type	Description	Default
topic_path	str	The topic path to match against the selector.	required

Returns:

Type	Description
bool	True if the path matches the selector; False otherwise.

any_of classmethod

any_of(*args: str) -> SelectorSet

Helper method that accepts selectors as individual arguments to create a set.

get_selector

get_selector(selector: str) -> Selector

Instantiate a selector based on the given textual value.

diffusion.features.topics.update

UpdateConstraint

Bases: abc.ABC, GenericModel

The constraint to be applied to an update operation or the creation of an update stream.

Notes

Constraints describe a condition that must be satisfied for an operation to succeed. Constraints can be applied to the setting of a value or creation of an update stream. Constraints are only evaluated on the server.

The constraints are evaluated using the:

• active session locks
• existence of the topic
• current value of the topic

The value of a topic can be described in several ways. The value can be described as an exact value, a partial value or an unset value.

Constraints can be composed with one another. It is only possible to construct logical ANDs of constraints. Constraints can only be composed if the resulting constraint is satisfiable. Multiple session locks can be held but a topic can only have a single value. Constraints specifying multiple topic values can't be constructed.

Constraints can be created using a ConstraintFactory.

__and__

__and__(other: UpdateConstraint) -> UpdateConstraint

Creates a composed constraint that represents a logical AND of this constraint and another.

Notes

You must use the binary & form to invoke this due to short-circuiting.

Parameters:

Name	Type	Description	Default
other	UpdateConstraint	The constraint that will be logically-ANDed with the current constraint.	required

Returns:

Type	Description
UpdateConstraint	The newly composed constraint that represents a logical AND of the current constraint and the other constraint.

constraint_factory

ConstraintFactory

Bases: abc.ABC

The factory for the update constraint types.

json_value property

json_value: PartialJSON

Gets the constraint that partially matches the current topic value.

Notes

The topic must be a diffusion.datatypes.JSON topic. The diffusion.features.topics.update.constraints.PartialJSON partially describes the structure of a diffusion.datatypes.JSON value.

Returns:

Type	Description
PartialJSON	The constraint.

no_value property

no_value: NoValueConstraint

Gets the constraint requiring the topic to have no value.

Notes

This is useful when setting the first value of a topic. This constraint is unsatisfied if no topic is present at the path, making it unsuitable for operations that try to add topics.

Returns:

Type	Description
NoValueConstraint	The constraint.

no_topic property

no_topic: NoTopicConstraint

Gets the constraint requiring the path to have no topic.

Notes

This is useful when setting the first value of a topic being added using Topics.add_and_set_topic without changing the value if the topic already exists. This constraint is unsatisfied if a topic is present at the path, making it unsuitable for operations that try to set topics without adding them.

Returns:

Type	Description
NoTopicConstraint	The constraint.

value

value(value: typing.Union[AbstractDataType, bytes]) -> BinaryValueConstraint

Creates a constraint requiring the current value of the topic to match the supplied value.

Notes

When a None value, the topic is set to have no value. Use the NoValueConstraint constraint to check if the topic has no value.

This is useful when changing the value of a topic. This constraint is unsatisfied if no topic is present at the path, making it unsuitable for operations that try to add topics.

Parameters:

Name	Type	Description	Default
value	typing.Union[AbstractDataType, bytes]	The value.	required

Returns:

Type	Description
BinaryValueConstraint	The update constraint.

constraints

PartialJSONType module-attribute

PartialJSONType = typing.TypeVar('PartialJSONType')

Instance of PartialJSON or any subclasses

Unconstrained

Bases: UpdateConstraint

The unconstrained update constraint.

BinaryValueConstraint

Bases: UpdateConstraint

The update constraint that requires the exact binary value.

NoValueConstraint

Bases: UpdateConstraint

The update constraint that requires a topic to have no value.

LockConstraint

Bases: UpdateConstraint

The constraint on a SessionLock

NoTopicConstraint

Bases: UpdateConstraint

The update constraint that requires the path to have no topic.

PartialJSON

Bases: UpdateConstraint

The constraint requiring the current value of the JSON topic to match the partially described value.

with_

with_(pointer: pydantic.StrictStr, value: AbstractDataType) -> 'PartialJSONType'

Requires a value at a specific position in the JSON object.

Notes

The pointer is a JSON Pointer (https://tools.ietf.org/html/rfc6901) syntax reference locating the value in the JSON object.

The pointer syntax is not being verified for correctness.

Parameters:

Name	Type	Description	Default
pointer	pydantic.StrictStr	The pointer expression.	required
value	AbstractDataType	The value.	required

Returns:

Type	Description
'PartialJSONType'	The constraint including the specified pointer.

without

without(pointer: pydantic.StrictStr) -> 'PartialJSONType'

Requires a specific position in the JSON object to be empty.

Notes

The pointer is a JSON Pointer (https://tools.ietf.org/html/rfc6901) syntax reference that should have no value in the JSON object.

The pointer syntax is not being verified for correctness.

Parameters:

Name	Type	Description	Default
pointer	pydantic.StrictStr	The pointer expression.	required

Returns:

Type	Description
'PartialJSONType'	The constraint including the specified pointer.