Python SDK

Official SDK

This SDK is officially developed and maintained by the native web GmbH, the creators of EventSourcingDB. It is aligned with the latest platform features and receives regular updates.

Installation#

To install the SDK, run:

pip install eventsourcingdb

You can also find this SDK on PyPI.

Capabilities#

This SDK intentionally focuses on application-level use cases. It provides core functionality for writing, reading, and observing events, and deliberately excludes operational concerns such as backup, restore, or health monitoring.

For a detailed explanation of the specific requirements behind each capability, see the Compliance Criteria.

Compatibility

Python SDK 1.5 runs with EventSourcingDB 1.0 and later.

Essentials

✓ Initialize the Client
✓ Ping the Server
✓ Verify API Token

Writing Events

✓ Write Single Events
✓ Write Multiple Events
✓ Use isSubjectPristine
✓ Use isSubjectOnEventId
Added in 1.4Requires EventSourcingDB 1.1✓ Use isEventQlQueryTrue
✓ Include OpenTelemetry Trace Context

Reading Events

✓ Read Events by Subject
✓ Read Recursively
✓ Read Chronological and Anti-Chronological
✓ Use Boundaries
✓ Use fromLatestEvent

Using EventQL

✓ Execute EventQL Queries

Observing Events

✓ Observe Events By Subject
✓ Observe Recursively
✓ Use Boundaries
✓ Use fromLatestEvent

Metadata and Discovery

✓ Register Event Schemas
✓ List Subjects
✓ List Event Types
Added in 1.5Requires EventSourcingDB 1.1✓ List a Specific Event Type

Testcontainers Support

✓ Start and Stop EventSourcingDB in Tests
✓ Use Custom Configuration (e.g., API Token, Port, …)

Getting Started#

Import the Client class and create an instance by providing the URL of your EventSourcingDB instance and the API token to use:

from eventsourcingdb import Client

url = 'http://localhost:3000'
api_token = 'secret'

client = Client(
  base_url = url,
  api_token = api_token,
)

Then call the ping function to check whether the instance is reachable. If it is not, the function will raise an error:

await client.ping()

Note that ping does not require authentication, so the call may succeed even if the API token is invalid.

If you want to verify the API token, call verify_api_token. If the token is invalid, the function will raise an error:

await client.verify_api_token()

Writing Events#

Call the write_events function and hand over a list with one or more events. You do not have to provide all event fields – some are automatically added by the server.

Specify source, subject, type, and data according to the CloudEvents format.

The function returns the written events, including the fields added by the server:

written_events = await client.write_events(
  events = [
    {
      'source': 'https://library.eventsourcingdb.io',
      'subject': '/books/42',
      'type': 'io.eventsourcingdb.library.book-acquired',
      'data': {
        'title': '2001 – A Space Odyssey',
        'author': 'Arthur C. Clarke',
        'isbn': '978-0756906788',
      },
    }
  ]
)

Using the `isSubjectPristine` precondition#

If you only want to write events in case a subject (such as /books/42) does not yet have any events, import the IsSubjectPristine class and pass it as the second argument as a list of preconditions:

from eventsourcingdb import IsSubjectPristine

written_events = await client.write_events(
  events = [
    # events
  ],
  preconditions = [
    IsSubjectPristine('/books/42')
  ],
)

Using the `isSubjectOnEventId` precondition#

If you only want to write events in case the last event of a subject (such as /books/42) has a specific ID (e.g., 0), import the IsSubjectOnEventId class and pass it as a list of preconditions in the second argument:

from eventsourcingdb import IsSubjectOnEventId

written_events = await client.write_events(
  events = [
    # events
  ],
  preconditions = [
    IsSubjectOnEventId('/books/42', '0')
  ],
)

Note that according to the CloudEvents standard, event IDs must be of type string.

Using the `isEventQlQueryTrue` preconditionChanged in 1.5Requires EventSourcingDB 1.1#

If you want to write events depending on an EventQL query, import the IsEventQlQueryTrue class and pass it as a list of preconditions in the second argument:

from eventsourcingdb import IsEventQlQueryTrue

written_events = await client.write_events(
  events = [
    # events
  ],
  preconditions = [
    IsEventQlQueryTrue('FROM e IN events WHERE e.type == "io.eventsourcingdb.library.book-borrowed" PROJECT INTO COUNT() < 10')
  ],
)

Note that the query must return a single row with a single value, which is interpreted as a boolean.

Reading Events#

To read all events of a subject, call the read_events function with the subject as the first argument and an options object as the second argument. Set the recursive option to False. This ensures that only events of the given subject are returned, not events of nested subjects.

The function returns an asynchronous generator, which you can use e.g. inside an async for loop:

from eventsourcingdb import ReadEventsOptions

async for event in client.read_events(
  subject = '/books/42',
  options = ReadEventsOptions(
    recursive = False
  ),
):
  pass

Reading From Subjects Recursively#

If you want to read not only all the events of a subject, but also the events of all nested subjects, set the recursive option to True:

from eventsourcingdb import ReadEventsOptions

async for event in client.read_events(
  subject = '/books/42',
  options = ReadEventsOptions(
    recursive = True
  ),
):
  pass

This also allows you to read all events ever written. To do so, provide / as the subject and set recursive to True, since all subjects are nested under the root subject.

Reading in Anti-Chronological Order#

By default, events are read in chronological order. To read in anti-chronological order, provide the order option and set it to Order.ANTICHRONOLOGICAL:

from eventsourcingdb import (
  Order,
  ReadEventsOptions,
)

async for event in client.read_events(
  subject = '/books/42',
  options = ReadEventsOptions(
    recursive = False,
    order = Order.ANTICHRONOLOGICAL,
  ),
):
  pass

Note that you can also specify Order.CHRONOLOGICAL to explicitly enforce the default order.

Specifying Bounds#

Sometimes you do not want to read all events, but only a range of events. For that, you can specify the lower_bound and upper_bound options – either one of them or even both at the same time.

Specify the ID and whether to include or exclude it, for both the lower and upper bound:

from eventsourcingdb import (
  Bound,
  BoundType,
  ReadEventsOptions,
)

async for event in client.read_events(
  subject = '/books/42',
  options = ReadEventsOptions(
    recursive = False,
    lower_bound = Bound(id = '100', type = BoundType.INCLUSIVE),
    upper_bound = Bound(id = '200', type = BoundType.EXCLUSIVE),
  ),
):
  pass

Starting From the Latest Event of a Given Type#

To read starting from the latest event of a given type, provide the from_latest_event option and specify the subject, the type, and how to proceed if no such event exists.

Possible options are IfEventIsMissingDuringRead.READ_NOTHING, which skips reading entirely, or IfEventIsMissingDuringRead.READ_EVERYTHING, which effectively behaves as if from_latest_event was not specified:

from eventsourcingdb import (
  IfEventIsMissingDuringRead,
  ReadEventsOptions,
  ReadFromLatestEvent,
)

async for event in client.read_events(
  subject = '/books/42',
  options = ReadEventsOptions(
    recursive = False,
    from_latest_event = ReadFromLatestEvent(
      subject = '/books/42',
      type = 'io.eventsourcingdb.library.book-borrowed',
      if_event_is_missing = IfEventIsMissingDuringRead.READ_EVERYTHING,
    ),
  ),
):
  pass

Note that from_latest_event and lower_bound can not be provided at the same time.

Aborting Reading#

If you need to abort reading use break or return within the async for loop. However, this only works if there is currently an iteration going on.

To abort reading independently of that, store the generator in a variable, and close it explicitly:

from eventsourcingdb import ReadEventsOptions

events = client.read_events(
  subject = '/books/42',
  options = ReadEventsOptions(
    recursive = False,
  ),
)

async for event in events:
  pass

# Somewhere else, abort the generator, which will cause
# reading to end.
await events.aclose()

Running EventQL Queries#

To run an EventQL query, call the run_eventql_query function and provide the query as argument. The function returns an asynchronous generator, which you can use e.g. inside an async for loop:

async for row in client.run_eventql_query(
  query = '''
    FROM e IN events
    PROJECT INTO e
  ''',
):
  pass

Note that each row returned by the generator matches the projection specified in your query.

Aborting a Query#

If you need to abort a query use break or return within the async for loop. However, this only works if there is currently an iteration going on.

To abort the query independently of that, store the generator in a variable, and close it explicitly:

rows = client.run_eventql_query(
  query = '''
    FROM e IN events
    PROJECT INTO e
  ''',
)

async for row in rows:
  pass

# Somewhere else, abort the generator, which will cause
# the query to end.
await rows.aclose()

Observing Events#

To observe all events of a subject, call the observe_events function with the subject as the first argument and an options object as the second argument. Set the recursive option to False. This ensures that only events of the given subject are returned, not events of nested subjects.

The function returns an asynchronous generator, which you can use e.g. inside an async for loop:

from eventsourcingdb import ObserveEventsOptions

async for event in client.observe_events(
  subject = '/books/42',
  options = ObserveEventsOptions(
    recursive = False
  ),
):
  pass

Observing From Subjects Recursively#

If you want to observe not only all the events of a subject, but also the events of all nested subjects, set the recursive option to True:

from eventsourcingdb import ObserveEventsOptions

async for event in client.observe_events(
  subject = '/books/42',
  options = ObserveEventsOptions(
    recursive = True
  ),
):
  pass

This also allows you to observe all events ever written. To do so, provide / as the subject and set recursive to True, since all subjects are nested under the root subject.

Specifying Bounds#

Sometimes you do not want to observe all events, but only a range of events. For that, you can specify the lower_bound option.

Specify the ID and whether to include or exclude it:

from eventsourcingdb import (
  Bound,
  BoundType,
  ObserveEventsOptions,
)

async for event in client.observe_events(
  subject = '/books/42',
  options = ObserveEventsOptions(
    recursive = False,
    lower_bound = Bound(id = '100', type = BoundType.INCLUSIVE),
  ),
):
  pass

Starting From the Latest Event of a Given Type#

To observe starting from the latest event of a given type, provide the from_latest_event option and specify the subject, the type, and how to proceed if no such event exists.

Possible options are IfEventIsMissingDuringObserve.WAIT_FOR_EVENT, which waits for an event of the given type to happen, or IfEventIsMissingDuringObserve.READ_EVERYTHING, which effectively behaves as if from_latest_event was not specified:

from eventsourcingdb import (
  IfEventIsMissingDuringObserve,
  ObserveEventsOptions,
  ObserveFromLatestEvent,
)

async for event in client.observe_events(
  subject = '/books/42',
  options = ObserveEventsOptions(
    recursive = False,
    from_latest_event = ObserveFromLatestEvent(
      subject = '/books/42',
      type = 'io.eventsourcingdb.library.book-borrowed',
      if_event_is_missing = IfEventIsMissingDuringObserve.READ_EVERYTHING,
    ),
  ),
):
  pass

Note that from_latest_event and lower_bound can not be provided at the same time.

Aborting Observing#

If you need to abort observing use break or return within the async for loop. However, this only works if there is currently an iteration going on.

To abort observing independently of that, store the generator in a variable, and close it explicitly:

from eventsourcingdb import ObserveEventsOptions

events = client.observe_events(
  subject = '/books/42',
  options = ObserveEventsOptions(
    recursive = False
  ),
)

async for event in events:
  pass

# Somewhere else, abort the generator, which will cause
# observing to end.
await events.aclose()

Registering an Event Schema#

To register an event schema, call the register_event_schema function and hand over an event type and the desired schema:

await client.register_event_schema(
  event_type = 'io.eventsourcingdb.library.book-acquired',
  json_schema = {
    'type': 'object',
    'properties': {
      'title': { 'type': 'string' },
      'author': { 'type': 'string' },
      'isbn': { 'type': 'string' },
    },
    'required': [
      'title',
      'author',
      'isbn'
    ],
    'additionalProperties': False,
  },
)

Listing Subjects#

To list all subjects, call the read_subjects function with / as the base subject. The function returns an asynchronous generator, which you can use e.g. inside an async for loop:

async for subject in client.read_subjects(
  base_subject = '/'
):
  pass

If you only want to list subjects within a specific branch, provide the desired base subject instead:

async for subject in client.read_subjects(
  base_subject = '/books'
):
  pass

Aborting Listing#

If you need to abort listing use break or return within the async for loop. However, this only works if there is currently an iteration going on.

To abort listing independently of that, store the generator in a variable, and close it explicitly:

subjects = client.read_subjects(
  base_subject = '/'
)

async for subject in subjects:
  pass

# Somewhere else, abort the generator, which will cause
# reading to end.
await subjects.aclose()

Listing Event Types#

To list all event types, call the read_event_types function. The function returns an asynchronous generator, which you can use e.g. inside an async for loop:

async for event_type in client.read_event_types():
  pass

Aborting Listing#

If you need to abort listing use break or return within the async for loop. However, this only works if there is currently an iteration going on.

To abort listing independently of that, store the generator in a variable, and close it explicitly:

event_types = client.read_event_types()

async for event_type in event_types:
  pass

# Somewhere else, abort the generator, which will cause
# reading to end.
await event_types.aclose()

Listing a Specific Event TypeAdded in 1.5Requires EventSourcingDB 1.1#

To list a specific event type, call the read_event_type function with the event type as an argument. The function returns the detailed event type, which includes the schema:

event_type = await client.read_event_type("io.eventsourcingdb.library.book-acquired")

Using Testcontainers#

Import the Container class, create an instance, call the start function to run a test container, get a client, run your test code, and finally call the stop function to stop the test container:

from eventsourcingdb import Container

container = Container()
container.start()

client = container.get_client()

# ...

container.stop()

To check if the test container is running, call the is_running function:

is_running = container.is_running()

Configuring the Container Instance#

By default, Container uses the latest tag of the official EventSourcingDB Docker image. To change that, call the with_image_tag function:

container = (
  Container()
    .with_image_tag('1.0.0')
)

Similarly, you can configure the port to use and the API token. Call the with_port or the with_api_token function respectively:

container = (
  Container()
    .with_port(4000)
    .with_api_token('secret')
)

Configuring the Client Manually#

In case you need to set up the client yourself, use the following functions to get details on the container:

get_host() returns the host name
get_mapped_port() returns the port
get_base_url() returns the full URL of the container
get_api_token() returns the API token

Further Resources#

Repository: thenativeweb/eventsourcingdb-client-python
Registry: PyPI
License (MIT): License file
Issue tracker: GitHub Issues

Python SDK

Installation#

Capabilities#

Getting Started#

Writing Events#

Using the isSubjectPristine precondition#

Using the isSubjectOnEventId precondition#

Using the isEventQlQueryTrue preconditionChanged in 1.5Requires EventSourcingDB 1.1#

Reading Events#

Reading From Subjects Recursively#

Reading in Anti-Chronological Order#

Specifying Bounds#

Starting From the Latest Event of a Given Type#

Aborting Reading#

Running EventQL Queries#

Aborting a Query#

Observing Events#

Observing From Subjects Recursively#

Specifying Bounds#

Starting From the Latest Event of a Given Type#

Aborting Observing#

Registering an Event Schema#

Listing Subjects#

Aborting Listing#

Listing Event Types#

Aborting Listing#

Listing a Specific Event TypeAdded in 1.5Requires EventSourcingDB 1.1#

Using Testcontainers#

Configuring the Container Instance#

Configuring the Client Manually#

Further Resources#

Using the `isSubjectPristine` precondition#

Using the `isSubjectOnEventId` precondition#

Using the `isEventQlQueryTrue` preconditionChanged in 1.5Requires EventSourcingDB 1.1#