Pulsar Python client library is a wrapper over the existing C++ client library and exposes all of the same features. You can find the code in the Python directory of the C++ client code.
All the methods in producer, consumer, and reader of a Python client are thread-safe.
pdoc-generated API docs for the Python client are available here.
You can install the pulsar-client
library either via PyPi, using pip, or by building the library from source.
To install the pulsar-client
library as a pre-built package using the pip package manager:
$ pip install pulsar-client=={{pulsar:version_number}}
If you install the client libraries on Linux to support services like Pulsar functions or Avro serialization, you can install optional components alongside the pulsar-client
library.
# avro serialization $ pip install pulsar-client[avro]=='{{pulsar:version_number}}' # functions runtime $ pip install pulsar-client[functions]=='{{pulsar:version_number}}' # all optional components $ pip install pulsar-client[all]=='{{pulsar:version_number}}'
Installation via PyPi is available for the following Python versions:
Platform | Supported Python versions |
---|---|
MacOS 10.13 (High Sierra), 10.14 (Mojave) | 2.7, 3.7 |
Linux | 2.7, 3.4, 3.5, 3.6, 3.7, 3.8 |
To install the pulsar-client
library by building from source, follow instructions and compile the Pulsar C++ client library. That builds the Python binding for the library.
To install the built Python bindings:
$ git clone https://github.com/apache/pulsar $ cd pulsar/pulsar-client-cpp/python $ sudo python setup.py install
The complete Python API reference is available at api/python.
You can find a variety of Python code examples for the pulsar-client library.
The following example creates a Python producer for the my-topic
topic and sends 10 messages on that topic:
import pulsar client = pulsar.Client('pulsar://localhost:6650') producer = client.create_producer('my-topic') for i in range(10): producer.send(('Hello-%d' % i).encode('utf-8')) client.close()
The following example creates a consumer with the my-subscription
subscription name on the my-topic
topic, receives incoming messages, prints the content and ID of messages that arrive, and acknowledges each message to the Pulsar broker.
import pulsar client = pulsar.Client('pulsar://localhost:6650') consumer = client.subscribe('my-topic', 'my-subscription') while True: msg = consumer.receive() try: print("Received message '{}' id='{}'".format(msg.data(), msg.message_id())) # Acknowledge successful processing of the message consumer.acknowledge(msg) except: # Message failed to be processed consumer.negative_acknowledge(msg) client.close()
This example shows how to configure negative acknowledgement.
from pulsar import Client, schema client = Client('pulsar://localhost:6650') consumer = client.subscribe('negative_acks','test',schema=schema.StringSchema()) producer = client.create_producer('negative_acks',schema=schema.StringSchema()) for i in range(10): print('send msg "hello-%d"' % i) producer.send_async('hello-%d' % i, callback=None) producer.flush() for i in range(10): msg = consumer.receive() consumer.negative_acknowledge(msg) print('receive and nack msg "%s"' % msg.data()) for i in range(10): msg = consumer.receive() consumer.acknowledge(msg) print('receive and ack msg "%s"' % msg.data()) try: # No more messages expected msg = consumer.receive(100) except: print("no more msg") pass
You can use the Pulsar Python API to use the Pulsar reader interface. Here's an example:
# MessageId taken from a previously fetched message msg_id = msg.message_id() reader = client.create_reader('my-topic', msg_id) while True: msg = reader.read_next() print("Received message '{}' id='{}'".format(msg.data(), msg.message_id())) # No acknowledgment
In addition to subscribing a consumer to a single Pulsar topic, you can also subscribe to multiple topics simultaneously. To use multi-topic subscriptions, you can supply a regular expression (regex) or a List
of topics. If you select topics via regex, all topics must be within the same Pulsar namespace.
The following is an example:
import re consumer = client.subscribe(re.compile('persistent://public/default/topic-*'), 'my-subscription') while True: msg = consumer.receive() try: print("Received message '{}' id='{}'".format(msg.data(), msg.message_id())) # Acknowledge successful processing of the message consumer.acknowledge(msg) except: # Message failed to be processed consumer.negative_acknowledge(msg) client.close()
You can use different builtin schema types in Pulsar. All the definitions are in the pulsar.schema
package.
Schema | Notes |
---|---|
BytesSchema | Get the raw payload as a bytes object. No serialization/deserialization are performed. This is the default schema mode |
StringSchema | Encode/decode payload as a UTF-8 string. Uses str objects |
JsonSchema | Require record definition. Serializes the record into standard JSON payload |
AvroSchema | Require record definition. Serializes in AVRO format |
The schema definition is done through a class that inherits from pulsar.schema.Record
.
This class has a number of fields which can be of either pulsar.schema.Field
type or another nested Record
. All the fields are specified in the pulsar.schema
package. The fields are matching the AVRO fields types.
Field Type | Python Type | Notes |
---|---|---|
Boolean | bool | |
Integer | int | |
Long | int | |
Float | float | |
Double | float | |
Bytes | bytes | |
String | str | |
Array | list | Need to specify record type for items. |
Map | dict | Key is always String . Need to specify value type. |
Additionally, any Python Enum
type can be used as a valid field type.
When adding a field, you can use these parameters in the constructor.
Argument | Default | Notes |
---|---|---|
default | None | Set a default value for the field. Eg: a = Integer(default=5) |
required | False | Mark the field as “required”. It is set in the schema accordingly. |
class Example(Record): a = String() b = Integer() c = Array(String()) i = Map(String())
from enum import Enum class Color(Enum): red = 1 green = 2 blue = 3 class Example(Record): name = String() color = Color
class MySubRecord(Record): x = Integer() y = Long() z = String() class Example(Record): a = String() sub = MySubRecord()
Set the namespace for Avro Record schema using the special field _avro_namespace
.
class NamespaceDemo(Record): _avro_namespace = 'xxx.xxx.xxx' x = String() y = Integer()
The schema definition is like this.
{ 'name': 'NamespaceDemo', 'namespace': 'xxx.xxx.xxx', 'type': 'record', 'fields': [ {'name': 'x', 'type': ['null', 'string']}, {'name': 'y', 'type': ['null', 'int']} ] }
You can send messages using BytesSchema
, StringSchema
, AvroSchema
, and JsonSchema
.
Before the producer is created, the Pulsar broker validates that the existing topic schema is the correct type and that the format is compatible with the schema definition of a class. If the format of the topic schema is incompatible with the schema definition, an exception occurs in the producer creation.
Once a producer is created with a certain schema definition, it only accepts objects that are instances of the declared schema class.
Similarly, for a consumer or reader, the consumer returns an object (which is an instance of the schema record class) rather than raw bytes.
Example
consumer = client.subscribe( topic='my-topic', subscription_name='my-subscription', schema=AvroSchema(Example) ) while True: msg = consumer.receive() ex = msg.value() try: print("Received message a={} b={} c={}".format(ex.a, ex.b, ex.c)) # Acknowledge successful processing of the message consumer.acknowledge(msg) except: # Message failed to be processed consumer.negative_acknowledge(msg)
You can send byte data using a BytesSchema
.
Example
producer = client.create_producer( 'bytes-schema-topic', schema=BytesSchema()) producer.send(b"Hello") consumer = client.subscribe( 'bytes-schema-topic', 'sub', schema=BytesSchema()) msg = consumer.receive() data = msg.value()
You can send string data using a StringSchema
.
Example
producer = client.create_producer( 'string-schema-topic', schema=StringSchema()) producer.send("Hello") consumer = client.subscribe( 'string-schema-topic', 'sub', schema=StringSchema()) msg = consumer.receive() str = msg.value()
You can declare an AvroSchema
using one of the following methods.
You can declare an AvroSchema
by passing a class that inherits from pulsar.schema.Record
and defines the fields as class variables.
Example
class Example(Record): a = Integer() b = Integer() producer = client.create_producer( 'avro-schema-topic', schema=AvroSchema(Example)) r = Example(a=1, b=2) producer.send(r) consumer = client.subscribe( 'avro-schema-topic', 'sub', schema=AvroSchema(Example)) msg = consumer.receive() e = msg.value()
You can declare an AvroSchema
using JSON. In this case, Avro schemas are defined using JSON.
Example
Below is an AvroSchema
defined using a JSON file (company.avsc).
{ "doc": "this is doc", "namespace": "example.avro", "type": "record", "name": "Company", "fields": [ {"name": "name", "type": ["null", "string"]}, {"name": "address", "type": ["null", "string"]}, {"name": "employees", "type": ["null", {"type": "array", "items": { "type": "record", "name": "Employee", "fields": [ {"name": "name", "type": ["null", "string"]}, {"name": "age", "type": ["null", "int"]} ] }}]}, {"name": "labels", "type": ["null", {"type": "map", "values": "string"}]} ] }
You can load a schema definition from file by using [avro.schema
]((http://avro.apache.org/docs/current/gettingstartedpython.html) or fastavro.schema
.
If you use the “JSON definition” method to declare an AvroSchema
, pay attention to the following points:
You need to use Python dict to produce and consume messages, which is different from using the “Record” method.
When generating an AvroSchema
object, set _record_cls
parameter to None
.
Example
from fastavro.schema import load_schema from pulsar.schema import * schema_definition = load_schema("examples/company.avsc") avro_schema = AvroSchema(None, schema_definition=schema_definition) producer = client.create_producer( topic=topic, schema=avro_schema) consumer = client.subscribe(topic, 'test', schema=avro_schema) company = { "name": "company-name" + str(i), "address": 'xxx road xxx street ' + str(i), "employees": [ {"name": "user" + str(i), "age": 20 + i}, {"name": "user" + str(i), "age": 30 + i}, {"name": "user" + str(i), "age": 35 + i}, ], "labels": { "industry": "software" + str(i), "scale": ">100", "funds": "1000000.0" } } producer.send(company) msg = consumer.receive() # Users could get a dict object by `value()` method. msg.value()
You can declare a JsonSchema
by passing a class that inherits from pulsar.schema.Record
and defines the fields as class variables. This is similar to using AvroSchema
. The only difference is to use JsonSchema
instead of AvroSchema
when defining schema type as shown below. For how to use AvroSchema
via record, see here.
producer = client.create_producer( 'avro-schema-topic', schema=JsonSchema(Example)) consumer = client.subscribe( 'avro-schema-topic', 'sub', schema=JsonSchema(Example))
End-to-end encryption allows applications to encrypt messages at producers and decrypt messages at consumers.
To use the end-to-end encryption feature in the Python client, you need to configure publicKeyPath
and privateKeyPath
for both producer and consumer.
publicKeyPath: "./public.pem" privateKeyPath: "./private.pem"
This section provides step-by-step instructions on how to use the end-to-end encryption feature in the Python client.
Prerequisite
Step
Create both public and private key pairs.
Input
openssl genrsa -out private.pem 2048 openssl rsa -in private.pem -pubout -out public.pem
Create a producer to send encrypted messages.
Input
import pulsar publicKeyPath = "./public.pem" privateKeyPath = "./private.pem" crypto_key_reader = pulsar.CryptoKeyReader(publicKeyPath, privateKeyPath) client = pulsar.Client('pulsar://localhost:6650') producer = client.create_producer(topic='encryption', encryption_key='encryption', crypto_key_reader=crypto_key_reader) producer.send('encryption message'.encode('utf8')) print('sent message') producer.close() client.close()
Create a consumer to receive encrypted messages.
Input
import pulsar publicKeyPath = "./public.pem" privateKeyPath = "./private.pem" crypto_key_reader = pulsar.CryptoKeyReader(publicKeyPath, privateKeyPath) client = pulsar.Client('pulsar://localhost:6650') consumer = client.subscribe(topic='encryption', subscription_name='encryption-sub', crypto_key_reader=crypto_key_reader) msg = consumer.receive() print("Received msg '{}' id = '{}'".format(msg.data(), msg.message_id())) consumer.close() client.close()
Run the consumer to receive encrypted messages.
Input
python consumer.py
In a new terminal tab, run the producer to produce encrypted messages.
Input
python producer.py
Now you can see the producer sends messages and the consumer receives messages successfully.
Output
This is from the producer side.
sent message
This is from the consumer side.
Received msg 'encryption message' id = '(0,0,-1,-1)'