testbed/dpkp__kafka-python/docs/index.rst

kafka-python
############

.. image:: https://img.shields.io/badge/kafka-2.6%2C%202.5%2C%202.4%2C%202.3%2C%202.2%2C%202.1%2C%202.0%2C%201.1%2C%201.0%2C%200.11%2C%200.10%2C%200.9%2C%200.8-brightgreen.svg
    :target: https://kafka-python.readthedocs.io/compatibility.html
.. image:: https://img.shields.io/pypi/pyversions/kafka-python.svg
    :target: https://pypi.python.org/pypi/kafka-python
.. image:: https://coveralls.io/repos/dpkp/kafka-python/badge.svg?branch=master&service=github
    :target: https://coveralls.io/github/dpkp/kafka-python?branch=master
.. image:: https://travis-ci.org/dpkp/kafka-python.svg?branch=master
    :target: https://travis-ci.org/dpkp/kafka-python
.. image:: https://img.shields.io/badge/license-Apache%202-blue.svg
    :target: https://github.com/dpkp/kafka-python/blob/master/LICENSE

Python client for the Apache Kafka distributed stream processing system.
kafka-python is designed to function much like the official java client, with a
sprinkling of pythonic interfaces (e.g., consumer iterators).

kafka-python is best used with newer brokers (0.9+), but is backwards-compatible with
older versions (to 0.8.0). Some features will only be enabled on newer brokers.
For example, fully coordinated consumer groups -- i.e., dynamic
partition assignment to multiple consumers in the same group -- requires use of
0.9 kafka brokers. Supporting this feature for earlier broker releases would
require writing and maintaining custom leadership election and membership /
health check code (perhaps using zookeeper or consul). For older brokers, you
can achieve something similar by manually assigning different partitions to
each consumer instance with config management tools like chef, ansible, etc.
This approach will work fine, though it does not support rebalancing on
failures.  See `Compatibility <compatibility.html>`_ for more details.

Please note that the master branch may contain unreleased features. For release
documentation, please see readthedocs and/or python's inline help.

>>> pip install kafka-python


KafkaConsumer
*************

:class:`~kafka.KafkaConsumer` is a high-level message consumer, intended to
operate as similarly as possible to the official java client. Full support
for coordinated consumer groups requires use of kafka brokers that support the
Group APIs: kafka v0.9+.

See `KafkaConsumer <apidoc/KafkaConsumer.html>`_ for API and configuration details.

The consumer iterator returns ConsumerRecords, which are simple namedtuples
that expose basic message attributes: topic, partition, offset, key, and value:

>>> from kafka import KafkaConsumer
>>> consumer = KafkaConsumer('my_favorite_topic')
>>> for msg in consumer:
...     print (msg)

>>> # join a consumer group for dynamic partition assignment and offset commits
>>> from kafka import KafkaConsumer
>>> consumer = KafkaConsumer('my_favorite_topic', group_id='my_favorite_group')
>>> for msg in consumer:
...     print (msg)

>>> # manually assign the partition list for the consumer
>>> from kafka import TopicPartition
>>> consumer = KafkaConsumer(bootstrap_servers='localhost:1234')
>>> consumer.assign([TopicPartition('foobar', 2)])
>>> msg = next(consumer)

>>> # Deserialize msgpack-encoded values
>>> consumer = KafkaConsumer(value_deserializer=msgpack.loads)
>>> consumer.subscribe(['msgpackfoo'])
>>> for msg in consumer:
...     assert isinstance(msg.value, dict)


KafkaProducer
*************

:class:`~kafka.KafkaProducer` is a high-level, asynchronous message producer.
The class is intended to operate as similarly as possible to the official java
client. See `KafkaProducer <apidoc/KafkaProducer.html>`_ for more details.

>>> from kafka import KafkaProducer
>>> producer = KafkaProducer(bootstrap_servers='localhost:1234')
>>> for _ in range(100):
...     producer.send('foobar', b'some_message_bytes')

>>> # Block until a single message is sent (or timeout)
>>> future = producer.send('foobar', b'another_message')
>>> result = future.get(timeout=60)

>>> # Block until all pending messages are at least put on the network
>>> # NOTE: This does not guarantee delivery or success! It is really
>>> # only useful if you configure internal batching using linger_ms
>>> producer.flush()

>>> # Use a key for hashed-partitioning
>>> producer.send('foobar', key=b'foo', value=b'bar')

>>> # Serialize json messages
>>> import json
>>> producer = KafkaProducer(value_serializer=lambda v: json.dumps(v).encode('utf-8'))
>>> producer.send('fizzbuzz', {'foo': 'bar'})

>>> # Serialize string keys
>>> producer = KafkaProducer(key_serializer=str.encode)
>>> producer.send('flipflap', key='ping', value=b'1234')

>>> # Compress messages
>>> producer = KafkaProducer(compression_type='gzip')
>>> for i in range(1000):
...     producer.send('foobar', b'msg %d' % i)


Thread safety
*************

The KafkaProducer can be used across threads without issue, unlike the
KafkaConsumer which cannot.

While it is possible to use the KafkaConsumer in a thread-local manner,
multiprocessing is recommended.


Compression
***********

kafka-python supports the following compression formats:

 - gzip
 - LZ4
 - Snappy
 - Zstandard (zstd)

gzip is supported natively, the others require installing additional libraries.
See `Install <install.html>`_ for more information.


Optimized CRC32 Validation
**************************

Kafka uses CRC32 checksums to validate messages. kafka-python includes a pure
python implementation for compatibility. To improve performance for high-throughput
applications, kafka-python will use `crc32c` for optimized native code if installed.
See `Install <install.html>`_ for installation instructions and
https://pypi.org/project/crc32c/ for details on the underlying crc32c lib.


Protocol
********

A secondary goal of kafka-python is to provide an easy-to-use protocol layer
for interacting with kafka brokers via the python repl. This is useful for
testing, probing, and general experimentation. The protocol support is
leveraged to enable a :meth:`~kafka.KafkaClient.check_version()`
method that probes a kafka broker and
attempts to identify which version it is running (0.8.0 to 2.6+).


.. toctree::
   :hidden:
   :maxdepth: 2

   Usage Overview <usage>
   API </apidoc/modules>
   install
   tests
   compatibility
   support
   license
   changelog