Pulsar Python client

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.

Install

You can install the pulsar-client library either via PyPi, using pip, or by building the library from source.

Install using pip

To install the pulsar-client library as a pre-built package using the pip package manager:

pip install pulsar-client==2.9.4

Optional dependencies

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]==2.9.4'

# functions runtime
pip install 'pulsar-client[functions]==2.9.4'

# all optional components
pip install 'pulsar-client[all]==2.9.4'

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

Install from source

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

API Reference

The complete Python API reference is available at api/python.

Examples

You can find a variety of Python code examples for the pulsar-client library.

Producer example

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()

Consumer example

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

Reader interface example

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

Multi-topic subscriptions

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()

Schema

Declare and validate schema

You can declare a schema by passing a class that inherits from pulsar.schema.Record and defines the fields as class variables. For example:

from pulsar.schema import *

class Example(Record):
    a = String()
    b = Integer()
    c = Boolean()

With this simple schema definition, you can create producers, consumers and readers instances that refer to that.

producer = client.create_producer(
                    topic='my-topic',
                    schema=AvroSchema(Example) )

producer.send(Example(a='Hello', b=1))

After creating the producer, the Pulsar broker validates that the existing topic schema is indeed of "Avro" type and that the format is compatible with the schema definition of the Example class.

If there is a mismatch, an exception occurs in the producer creation.

Once a producer is created with a certain schema definition, it will only accept objects that are instances of the declared schema class.

Similarly, for a consumer/reader, the consumer will return an object, instance of the schema record class, rather than the raw bytes:

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)

Supported schema types

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

Schema definition reference

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.

Fields parameters

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.

Schema definition examples

Simple definition

class Example(Record):
    a = String()
    b = Integer()
    c = Array(String())
    i = Map(String())

Using enums

from enum import Enum

class Color(Enum):
    red = 1
    green = 2
    blue = 3

class Example(Record):
    name = String()
    color = Color

Complex types

class MySubRecord(Record):
    x = Integer()
    y = Long()
    z = String()

class Example(Record):
    a = String()
    sub = MySubRecord()

Set namespace for Avro schema

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']}
  ]
}

End-to-end encryption

End-to-end encryption allows applications to encrypt messages at producers and decrypt messages at consumers.

Configuration

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"

Tutorial

This section provides step-by-step instructions on how to use the end-to-end encryption feature in the Python client.

Prerequisite

Pulsar Python client 2.7.1 or later

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)'
```

Install​

Install using pip​

Optional dependencies​

Install from source​

API Reference​

Examples​

Producer example​

Consumer example​

Reader interface example​

Multi-topic subscriptions​

Schema​

Declare and validate schema​

Supported schema types​

Schema definition reference​

Fields parameters​

Schema definition examples​

Simple definition​

Using enums​

Complex types​

Set namespace for Avro schema​

End-to-end encryption​

Configuration​

Tutorial​

Install

Install using pip

Optional dependencies

Install from source

API Reference

Examples

Producer example

Consumer example

Reader interface example

Multi-topic subscriptions

Schema

Declare and validate schema

Supported schema types

Schema definition reference

Fields parameters

Schema definition examples

Simple definition

Using enums

Complex types

Set namespace for Avro schema

End-to-end encryption

Configuration

Tutorial