Publish/Subscribe API for PubNub Python-Tornado SDK
Python version support
Python SDK versions 5.0.0 and higher no longer support Python v2.7 and the Twisted and Tornado frameworks. If you require support for any of these, use SDK version 4.8.1.
Note that PubNub will stop supporting versions of Python lower than 3.7 by the end of 2021.
Publish
Description
The publish()
function is used to send a message to all subscribers of a channel. To publish a message you must first specify a valid publish_key
at initialization. A successfully published message is replicated across the PubNub Real-Time Network and sent simultaneously to all subscribed clients on a channel.
Messages in transit can be secured from potential eavesdroppers with SSL/TLS by setting ssl to true during initialization.
Important
The new Jackson parser does not recognize JSONObject. Please use ObjectNode instead.
Publish Anytime
It's not required to be subscribed to a channel in order to publish to that channel.
Message Data:
The message argument can contain any JSON serializable data, including: Objects, Arrays, Ints and Strings. data
should not contain special Python-Tornado classes or functions as these will not serialize. String content can include any single-byte or multi-byte UTF-8 character.
Don't JSON serialize!
It is important to note that you should not JSON serialize when sending signals/messages via PUBNUB. Why? Because the serialization is done for you automatically. Instead just pass the full object as the message payload. PubNub takes care of everything for you.
Message Size:
The maximum number of characters per message is 32 KiB by default. The maximum message size is based on the final escaped character count, including the channel name. An ideal message size is under 1800 bytes which allows a message to be compressed and sent using single IP datagram (1.5 KiB) providing optimal network performance.
If the message you publish exceeds the configured size, you will receive the following message:
Message Too Large Error
["PUBLISHED",[0,"Message Too Large","13524237335750949"]]
For further details please check: https://support.pubnub.com/hc/en-us/articles/360051495932-Calculating-Message-Payload-Size-Before-Publish
Message Publish Rate:
Messages can be published as fast as bandwidth conditions will allow. There is a soft limit based on max throughput since messages will be discarded if the subscriber can't keep pace with the publisher.
For example, if 200 messages are published simultaneously before a subscriber has had a chance to receive any messages, the subscriber may not receive the first 100 messages because the message queue has a limit of only 100 messages stored in memory.
Publishing to Multiple Channels:
It is not possible to publish a message to multiple channels simultaneously. The message must be published to one channel at a time.
Publishing Messages Reliably:
There are some best practices to ensure messages are delivered when publishing to a channel:
- Publish to any given channel in a serial manner (not concurrently).
- Check that the return code is success (e.g.
[1,"Sent","136074940..."]
) - Publish the next message only after receiving a success return code.
- If a failure code is returned (
[0,"blah","<timetoken>"]
), retry the publish. - Avoid exceeding the in-memory queue's capacity of 100 messages. An overflow situation (aka missed messages) can occur if slow subscribers fail to keep up with the publish pace in a given period of time.
- Throttle publish bursts in accordance with your app's latency needs e.g. Publish no faster than 5 msgs per second to any one channel.
Method(s)
To Publish a message
you can use the following method(s) in the Python-Tornado SDK:
pubnub.publish().channel(String).message(Object).should_store(Boolean).meta(dict).use_post(Boolean)
Parameter Type Required Defaults Description channel
String Yes Destination of message
.message
Object Yes The payload. should_store
Boolean Optional account default
Store in history meta
Object Optional None
Meta data object which can be used with the filtering ability.
Basic Usage
Publish a message to a channel:
from pubnub.exceptions import PubNubException
try:
envelope = yield pubnub.publish().channel("my_channel").message({
'name': 'Alex',
'online': True
}).future()
print("publish timetoken: %d" % envelope.result.timetoken)
except PubNubException as e:
handle_exception(e)
Note
Before running the above publish example, either using the Debug Console or in a separate script running in a separate terminal window, subscribe to the same channel that is being published to.
Returns
The publish()
operation returns a PNPublishResult
which contains the following fields:
Field | Type | Description |
---|---|---|
timetoken | Int | an int representation of the timetoken when the message was published |
Other Examples
-
envelope = yield pubnub.publish()\ .channel("my_channel")\ .message(["hello", "there"])\ .meta({'name': 'Alex'})\ .future() # handle publish result, status always present, result if successful # envelope.status.is_error() to see if error happened
Fire
Description
The fire endpoint allows the client to send a message to PubNub Functions Event Handlers. These messages will go directly to any Event Handlers registered on the channel that you fire to and will trigger their execution. The content of the fired request will be available for processing within the Event Handler. The message sent via fire()
isn't replicated, and so won't be received by any subscribers to the channel. The message is also not stored in history.
Method(s)
To Fire a message
you can use the following method(s) in the Python-Tornado SDK:
pubnub.fire().channel(String).message(Object).meta(Object).use_post(Boolean)
Parameter | Type | Required | Defaults | Description |
---|---|---|---|---|
channel | String | Yes | Destination of message . | |
message | Object | Yes | The payload. | |
use_post | Boolean | Optional | false | Use POST to publish. |
meta | Object | Optional | None | Meta data object which can be used with the filtering ability. |
Basic Usage
Fire a message to a channel:
envelope = yield pubnub.fire().channel('my_channel').message('hello there').use_post(true).future()
print('fire timetoken: %d' % envelope.result.timetoken)
Signal
Description
The signal()
function is used to send a signal to all subscribers of a channel.
By default, signals are limited to a message payload size of 64
bytes. This limit applies only to the payload, and not to the URI or headers. If you require a larger payload size, please contact support.
Method(s)
To Signal a message
you can use the following method(s) in the Python-Tornado SDK:
pubnub.signal().message(Object).channel(String)
Parameter Type Required Description message
Object Yes The payload. channel
String Yes Destination of message
.
Basic Usage
Signal a message to a channel:
envelope = yield pubnub.signal().channel('some_channel').message('foo').future()
Response
Field | Type | Description |
---|---|---|
timetoken | int | An int representation of the timetoken when Signal was sent. |
Subscribe
Description
This function causes the client to create an open TCP socket to the PubNub Real-Time Network and begin listening for messages on a specified channel
. To subscribe to a channel
the client must send the appropriate subscribe_key
at initialization.
By default a newly subscribed client will only receive messages published to the channel after the subscribe()
call completes.
If a client gets disconnected from a channel, it can automatically attempt to reconnect to that channel
and retrieve any available messages that were missed during that period. This can be achieved by setting setReconnectionPolicy
to PNReconnectionPolicy.LINEAR
, when initializing the client.
Warning
Unsubscribing from all channels, and then subscribing to a new channel Y is not the same as subscribing to channel Y and then unsubscribing from the previously-subscribed channel(s). Unsubscribing from all channels resets the last-received timetoken
and thus, there could be some gaps in the subscription that may lead to message loss.
Method(s)
To Subscribe to a channel
you can use the following method(s) in the Python-Tornado SDK:
pubnub.subscribe().channels(String|List|Tuple).channel_groups(String|List|Tuple).with_timetoken(Int).with_presence().execute()
Parameter Type Required Description channels
String | List | Tuple Optional Subscribe to channels
, Eitherchannel
orchannel_group
is required.channel_groups
String | List | Tuple Optional Subscribe to channel_groups
, Eitherchannel
orchannel_group
is required.timetoken
Int Optional Pass a timetoken
.with_presence
Command Optional Also subscribe to related presence information.
Basic Usage
Subscribe to a channel:
pubnub.subscribe().channels("my_channel").execute()
Note
The response of the call is handled by adding a Listener. Please see the Listeners section for more details. Listeners should be added before calling the method.
Returns
Note
PNMessageResult
is returned in the Listeners
The subscribe()
operation returns a PNStatus
for messages which contains the following fields:
Field | Type | Description |
---|---|---|
category | PNStatusCategory | Details of StatusCategory are here |
is_error | Boolean | This is true if an error occurred in the execution of the operation. |
error_data | PNErrorData | Error data of the exception (if Error is true ). |
status_code | int | Status code of the execution. |
The subscribe()
operation returns a PNMessageResult
for messages which contains the following fields:
Field | Type | Description |
---|---|---|
message | Object | The message sent on channel . |
subscription | String | The channel group or wildcard subscription match (if exists). |
channel | String | The channel for which the message belongs. |
timetoken | Int | Timetoken for the message. |
user_metadata | Dict | User metadata . |
The subscribe()
operation returns a PNPresenceEventResult
from presence which contains the following operations:
Field | Type | Description |
---|---|---|
event | String | Events like join , leave , timeout , state-change . |
uuid | String | uuid for event. |
timestamp | Int | timestamp for event. |
occupancy | Int | Current occupancy . |
subscription | String | The channel group or wildcard subscription match (if exists). |
channel | String | The channel for which the message belongs. |
timetoken | Int | timetoken of the message. |
user_metadata | Dict | User metadata . |
The subscribe()
operation returns a PNSignalResult
for signals which contains the following operations:
Field | Type | Description |
---|---|---|
timetoken | Int | An int representation of the timetoken when Signal was sent. |
channel | String | The channel on which Signal occurred. |
publisher | String | ID of the sender. |
message | Object | The payload. |
Other Examples
-
import logging import pubnub from pubnub.pnconfiguration import PNConfiguration from pubnub.pubnub_tornado import PubNubTornado from pubnub.pubnub_tornado import SubscribeListener pubnub.set_stream_logger('pubnub', logging.DEBUG) pnconfig = PNConfiguration() pnconfig.subscribe_key = 'demo' pnconfig.publish_key = 'demo' pubnub = PubNubTornado(pnconfig) pubnub.add_listener(SubscribeListener()) pubnub.subscribe().channels("my_channel").execute()
Subscribing to multiple channels:
It's possible to subscribe to more than one channel using the Multiplexing feature. The example shows how to do that using an array to specify the channel names.
Alternative subscription methods
You can also use Wildcard Subscribe and Channel Groups to subscribe to multiple channels at a time. To use these features, the Stream Controller add-on must be enabled on your keyset in the Admin Portal.
pubnub.subscribe().channels(["my_channel1", "my_channel2"]).execute()
- Subscribing to a Presence channel: Requires Presence add-onRequires that the Presence add-on is enabled for your key. See this page on enabling add-on features on your keys:
https://support.pubnub.com/hc/en-us/articles/360051974791-How-do-I-enable-add-on-features-for-my-keys-For any given channel there is an associated Presence channel. You can subscribe directly to the channel by appending
-pnpres
to the channel name. For example the channel namedmy_channel
would have the presence channel namedmy_channel-pnpres
.pubnub.subscribe()\ .channels("my_channel")\ .with_presence()\ .execute()
Sample Responses
Join Event
if envelope.event == 'join': envelope.uuid # 175c2c67-b2a9-470d-8f4b-1db94f90e39e envelope.timestamp # 1345546797 envelope.occupancy # 2
Leave Event
{ "action" : "leave", "timestamp" : 1345549797, "uuid" : "175c2c67-b2a9-470d-8f4b-1db94f90e39e", "occupancy" : 1 }
Timeout Event
if envelope.event == 'timeout': envelope.uuid # 175c2c67-b2a9-470d-8f4b-1db94f90e39e envelope.timestamp # 1345546797 envelope.occupancy # 0
Custom Presence Event (State Change)
if envelope.event == 'state-change': envelope.uuid # 76c2c571-9a2b-d074-b4f8-e93e09f49bd envelope.timestamp # 1345546797 envelope.user_metadata # {'is_typing': True}
Interval Event
{ "action":"interval", "timestamp":1474396578, "occupancy":2 }
When a channel is in interval mode with
presence_deltas
pnconfig
flag enabled, the interval message may also include the following fields which contain an array of changed UUIDs since the last interval message.- joined
- left
- timedout
For example, this interval message indicates there were 2 new UUIDs that joined and 1 timed out UUID since the last interval:
{ "action" : "interval", "occupancy" : <# users in channel>, "timestamp" : <unix timestamp>, "joined" : ["uuid2", "uuid3"], "timedout" : ["uuid1"] }
If the full interval message is greater than
30KB
(since the max publish payload is∼32KB
), none of the extra fields will be present. Instead there will be ahere_now_refresh
boolean field set totrue
. This indicates to the user that they should do ahereNow
request to get the complete list of users present in the channel.{ "action" : "interval", "occupancy" : <# users in channel>, "timestamp" : <unix timestamp>, "here_now_refresh" : true }
- Wildcard subscribe to channels: Requires Stream Controller add-onRequires that the Stream Controller add-on is enabled with Enable Wildcard Subscribe checked for your key. See this page on enabling add-on features on your keys:
https://support.pubnub.com/hc/en-us/articles/360051974791-How-do-I-enable-add-on-features-for-my-keys-Wildcard subscribes allow the client to subscribe to multiple channels using wildcard. For example, if you subscribe to
a.*
you will get all messages fora.b
,a.c
,a.x
. The wildcarded*
portion refers to any portion of the channel string name after thedot (.)
.pubnub.subscribe().channels("foo.*").execute();
Wildcard grants and revokes
Only one level (
a.*
) of wildcarding is supported. If you grant on*
ora.b.*
, the grant will treat*
ora.b.*
as a single channel named either*
ora.b.*
. You can also revoke permissions from multiple channels using wildcards but only if you previously granted permissions using the same wildcards. Wildcard revokes, similarly to grants, only work one level deep, likea.*
. - Subscribing with State: Requires Presence add-onRequires that the Presence add-on is enabled for your key. See this page on enabling add-on features on your keys:
https://support.pubnub.com/hc/en-us/articles/360051974791-How-do-I-enable-add-on-features-for-my-keys-Note
Always set the
UUID
to uniquely identify the user or device that connects to PubNub. ThisUUID
should be persisted, and should remain unchanged for the lifetime of the user or the device. If you don't set theUUID
, you won't be able to connect to PubNub.from pubnub.pubnub_tornado import PubNubTornado from pubnub.pubnub_tornado import SubscribeListener class MySubscribeListener(SubscribeListener): def __init__(self): pass def status(self, pubnub, status): if status.category == PNStatusCategory.PNConnectedCategory: state = { 'field_a': 'awesome', 'field_b': 10 } pubnub.ioloop.add_future( pubnub.set_state().channels('my_channel').\ channel_groups('awesome_channel_groups').state(state).future() ) else: pass def message(self, pubnub, message): pass def presence(self, pubnub, presence): pass pubnub = PubNubTornado(pnconfig) my_listener = MySubscribeListener() pubnub.add_listener(my_listener) pubnub.subscribe().channels("my_channel").execute()
- Subscribe to a channel group: Requires Stream Controller add-onRequires that the Stream Controller add-on is enabled for your key. See this page on enabling add-on features on your keys:
https://support.pubnub.com/hc/en-us/articles/360051974791-How-do-I-enable-add-on-features-for-my-keys-pubnub.subscribe().channel_groups("awesome_channel_group").execute()
- Subscribe to the presence channel of a channel group: Requires Stream Controller and Presence add-onRequires that both Stream Controller and Presence add-ons are enabled for your key. See this page on enabling add-on features on your keys:
https://support.pubnub.com/hc/en-us/articles/360051974791-How-do-I-enable-add-on-features-for-my-keys-pubnub.subscribe().channel_groups(["cg1", "cg2"]).with_presence().execute()
Unsubscribe
Description
When subscribed to a single channel, this function causes the client to issue a leave
from the channel
and close any open socket to the PubNub Network. For multiplexed channels, the specified channel
(s) will be removed and the socket remains open until there are no more channels remaining in the list.
Warning
Unsubscribing from all channels, and then subscribing to a new channel Y is not the same as subscribing to channel Y and then unsubscribing from the previously-subscribed channel(s). Unsubscribing from all channels resets the last-received timetoken
and thus, there could be some gaps in the subscription that may lead to message loss.
Method(s)
To Unsubscribe from a channel
you can use the following method(s) in the Python-Tornado SDK:
pubnub.unsubscribe().channels(String|List|Tuple).channel_groups(String|List|Tuple).execute()
Parameter Type Required Description channels
String | List | Tuple Optional Subscribe to channels
, Eitherchannel
orchannel_group
is required.channel_groups
String | List | Tuple Optional Subscribe to channel_groups
, Eitherchannel
orchannel_group
is required
Basic Usage
Unsubscribe from a channel:
pubnub.unsubscribe().channels("my_channel").execute()
Note
The response of the call is handled by adding a Listener. Please see the Listeners section for more details. Listeners should be added before calling the method.
Response
The output below demonstrates the response to a successful call:
if envelope.event == 'leave':
envelope.uuid # 175c2c67-b2a9-470d-8f4b-1db94f90e39e
envelope.timestamp # 1345546797
envelope.occupancy # 2
Other Examples
- Unsubscribing from multiple channels. Requires Stream Controller add-onRequires that the Stream Controller add-on is enabled for your key. See this page on enabling add-on features on your keys:
https://support.pubnub.com/hc/en-us/articles/360051974791-How-do-I-enable-add-on-features-for-my-keys-pubnub.unsubscribe().channels(["my_channel1", "my_channel2"]).execute();
{ "action" : "leave" }
Unsubscribe from a channel group
pubnub.unsubscribe().channels_groups(["my_group1", "my_group2").execute()
{ "action": "leave" }
Unsubscribe All
Description
Unsubscribe from all channels and all channel groups
Method(s)
pubnub.unsubscribe_all()
Basic Usage
pubnub.unsubscribe_all();
Returns
None
Listeners
Description
You can be notified of connectivity status, message and presence notifications via the listeners.
Listeners should be added before calling the method.
Adding Listeners
from pubnub.callbacks import SubscribeCallback
from pubnub.enums import PNOperationType, PNStatusCategory
class MySubscribeCallback(SubscribeCallback):
def status(self, pubnub, status):
# The status object returned is always related to subscribe but could contain
# information about subscribe, heartbeat, or errors
# use the operationType to switch on different options
if status.operation == PNOperationType.PNSubscribeOperation \
or status.operation == PNOperationType.PNUnsubscribeOperation:
if status.category == PNStatusCategory.PNConnectedCategory:
pass
# This is expected for a subscribe, this means there is no error or issue whatsoever
elif status.category == PNStatusCategory.PNReconnectedCategory:
pass
# This usually occurs if subscribe temporarily fails but reconnects. This means
# there was an error but there is no longer any issue
elif status.category == PNStatusCategory.PNDisconnectedCategory:
pass
# This is the expected category for an unsubscribe. This means there
# was no error in unsubscribing from everything
elif status.category == PNStatusCategory.PNUnexpectedDisconnectCategory:
pass
# This is usually an issue with the internet connection, this is an error, handle
# appropriately retry will be called automatically
elif status.category == PNStatusCategory.PNAccessDeniedCategory:
pass
# This means that PAM does not allow this client to subscribe to this
# channel and channel group configuration. This is another explicit error
else:
pass
# This is usually an issue with the internet connection, this is an error, handle appropriately
# retry will be called automatically
elif status.operation == PNOperationType.PNSubscribeOperation:
# Heartbeat operations can in fact have errors, so it is important to check first for an error.
# For more information on how to configure heartbeat notifications through the status
# PNObjectEventListener callback, consult http://www.pubnub.com/docs/sdks/python/tornado/api-reference/configuration#configuration
if status.is_error():
pass
# There was an error with the heartbeat operation, handle here
else:
pass
# Heartbeat operation was successful
else:
pass
# Encountered unknown status type
def presence(self, pubnub, presence):
pass # handle incoming presence data
def message(self, pubnub, message):
pass # handle incoming messages
def signal(self, pubnub, signal):
pass # handle incoming signals
pubnub.add_listener(MySubscribeCallback())
Removing Listeners
my_listener = MySubscribeCallback()
pubnub.add_listener(my_listener)
# some time later
pubnub.remove_listener(my_listener)
Handling Disconnects
from pubnub.callbacks import SubscribeCallback
from pubnub.enums import PNStatusCategory
class HandleDisconnectsCallback(SubscribeCallback):
def status(self, pubnub, status):
if status.category == PNStatusCategory.PNUnexpectedDisconnectCategory:
# internet got lost, do some magic and call reconnect when ready
pubnub.reconnect()
elif status.category == PNStatusCategory.PNTimeoutCategory:
# do some magic and call reconnect when ready
pubnub.reconnect()
else:
logger.debug(status)
def presence(self, pubnub, presence):
pass
def message(self, pubnub, message):
pass
def signal(self, pubnub, signal):
pass
disconnect_listener = HandleDisconnectsCallback()
pubnub.add_listener(disconnect_listener)
Listener status events
Category | Description |
---|---|
PNTimeoutCategory | Failure to establish a connection to PubNub due to a timeout. |
PNBadRequestCategory | The server responded with a bad response error because the request is malformed. |
PNNetworkIssuesCategory | A subscribe event experienced an exception when running. The SDK isn't able to reach the PubNub Data Stream Network. This may be due to many reasons, such as: the machine or device isn't connected to the internet; the internet connection has been lost; your internet service provider is having trouble; or, perhaps the SDK is behind a proxy. |
PNReconnectedCategory | The SDK was able to reconnect to PubNub. |
PNConnectedCategory | SDK subscribed with a new mix of channels. This is fired every time the channel or channel group mix changes. |
PNUnexpectedDisconnectCategory | Previously started subscribe loop did fail and at this moment client disconnected from real-time data channels. |
PNUnknownCategory | Returned when the subscriber gets a non-200 HTTP response code from the server. |
Note
SubscribeListener
should not be used with high-performance sections of your app.