Slack Developer Kit for Python
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Basic Usage

The Slack Web API allows you to build applications that interact with Slack in more complex ways than the integrations we provide out of the box.

Access Slack’s API methods requires an OAuth token – see the Tokens & Authentication section for more on how Slack uses OAuth tokens as well as best practices.

Each of these API methods is fully documented on our developer site at api.slack.com

Sending a message

One of the primary uses of Slack is posting messages to a channel using the channel ID or as a DM to another person using their user ID. This method will handle either a channel ID or a user ID passed to the channel parameter.

import logging
logging.basicConfig(level=logging.DEBUG)

import os
from slack import WebClient
from slack.errors import SlackApiError

slack_token = os.environ["SLACK_API_TOKEN"]
client = WebClient(token=slack_token)

try:
  response = client.chat_postMessage(
    channel="C0XXXXXX",
    text="Hello from your app! :tada:"
  )
except SlackApiError as e:
  # You will get a SlackApiError if "ok" is False
  assert e.response["error"]  # str like 'invalid_auth', 'channel_not_found'

Sending an ephemeral message, which is only visible to an assigned user in a specified channel, is nearly the same as sending a regular message, but with an additional user parameter.

See chat.postEphemeral for more info.


Formatting with Block Kit

Messages posted from apps can contain more than just text, though. They can include full user interfaces composed of blocks.

The chat.postMessage method takes an optional blocks argument that allows you to customize the layout of a message. Blocks specified in a single object literal, so just add additional keys for any optional argument.

To send a message to a channel, use the channel’s ID. For IMs, use the user’s ID.

client.chat_postMessage(
  channel="C0XXXXXX",
  blocks=[
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "Danny Torrence left the following review for your property:"
      }
    },
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "<https://example.com|Overlook Hotel> \n :star: \n Doors had too many axe holes, guest in room " +
          "237 was far too rowdy, whole place felt stuck in the 1920s."
      },
      "accessory": {
        "type": "image",
        "image_url": "https://images.pexels.com/photos/750319/pexels-photo-750319.jpeg",
        "alt_text": "Haunted hotel image"
      }
    },
    {
      "type": "section",
      "fields": [
        {
          "type": "mrkdwn",
          "text": "*Average Rating*\n1.0"
        }
      ]
    }
  ]
)

Note: You can use the Block Kit Builder to prototype your message’s look and feel.


Threading Messages

Threaded messages are a way of grouping messages together to provide greater context. You can reply to a thread or start a new threaded conversation by simply passing the original message’s ts ID in the thread_ts attribute when posting a message. If you’re replying to a threaded message, you’ll pass the thread_ts ID of the message you’re replying to.

A channel or DM conversation is a nearly linear timeline of messages exchanged between people, bots, and apps. When one of these messages is replied to, it becomes the parent of a thread. By default, threaded replies do not appear directly in the channel, instead relegated to a kind of forked timeline descending from the parent message.

response = client.chat_postMessage(
  channel="C0XXXXXX",
  thread_ts="1476746830.000003",
  text="Hello from your app! :tada:"
)

By default, reply_broadcast is set to False. To indicate your reply is germane to all members of a channel, and therefore a notification of the reply should be posted in-channel, set the reply_broadcast to True.

response = client.chat_postMessage(
  channel="C0XXXXXX",
  thread_ts="1476746830.000003",
  text="Hello from your app! :tada:",
  reply_broadcast=True
)

Note: While threaded messages may contain attachments and message buttons, when your reply is broadcast to the channel, it’ll actually be a reference to your reply, not the reply itself. So, when appearing in the channel, it won’t contain any attachments or message buttons. Also note that updates and deletion of threaded replies works the same as regular messages.

See the Threading messages together article for more information.


Updating a message

Let’s say you have a bot which posts the status of a request. When that request changes, you’ll want to update the message to reflect it’s state.

response = client.chat_update(
  channel="C0XXXXXX",
  ts="1476746830.000003",
  text="updates from your app! :tada:"
)

See chat.update for formatting options and some special considerations when calling this with a bot user.


Deleting a message

Sometimes you need to delete things.

response = client.chat_delete(
  channel="C0XXXXXX",
  ts="1476745373.000002"
)

See chat.delete for more info.


Opening a modal

Modals allow you to collect data from users and display dynamic information in a focused surface.

Modals use the same blocks that compose messages with the addition of an input block.

# This module is available since v2.6.0rc1
from slack.signature import SignatureVerifier
signature_verifier = SignatureVerifier(os.environ["SLACK_SIGNING_SECRET"])

from flask import Flask, request, make_response
app = Flask(__name__)

@app.route("/slack/events", methods=["POST"])
def slack_app():
  if not signature_verifier.is_valid_request(request.get_data(), request.headers):
    return make_response("invalid request", 403)

  if "command" in request.form \
    and request.form["command"] == "/open-modal":
    trigger_id = request.form["trigger_id"]
    try:
      response = client.views_open(
        trigger_id=trigger_id,
        view={
          "type": "modal",
          "callback_id": "modal-id",
          "title": {
            "type": "plain_text",
            "text": "Awesome Modal"
          },
          "submit": {
            "type": "plain_text",
            "text": "Submit"
          },
          "close": {
            "type": "plain_text",
            "text": "Cancel"
          },
          "blocks": [
            {
              "type": "input",
              "block_id": "b-id",
              "label": {
                "type": "plain_text",
                "text": "Input label",
              },
              "element": {
                "action_id": "a-id",
                "type": "plain_text_input",
              }
            }
          ]
        }
      )
      return make_response("", 200)
    except SlackApiError as e:
      code = e.response["error"]
      return make_response(f"Failed to open a modal due to {code}", 200)

  elif "payload" in request.form:
    payload = json.loads(request.form["payload"])
    if payload["type"] == "view_submission" \
      and payload["view"]["callback_id"] == "modal-id":
      submitted_data = payload["view"]["state"]["values"]
      print(submitted_data)  # {'b-id': {'a-id': {'type': 'plain_text_input', 'value': 'your input'}}}
      return make_response("", 200)

  return make_response("", 404)

if __name__ == "__main__":
  # export SLACK_SIGNING_SECRET=***
  # export SLACK_API_TOKEN=xoxb-***
  # export FLASK_ENV=development
  # python3 app.py
  app.run("localhost", 3000)

See views.open more details and additional parameters.


Updating and pushing modals

You can dynamically update a view inside of a modal by calling views.update and passing the view ID returned in the previous views.open call.

private_metadata = "any str data you want to store"
response = client.views_update(
  view_id=payload["view"]["id"],
  hash=payload["view"]["hash"],
  view={
    "type": "modal",
    "callback_id": "modal-id",
    "private_metadata": private_metadata,
    "title": {
      "type": "plain_text",
      "text": "Awesome Modal"
    },
    "submit": {
      "type": "plain_text",
      "text": "Submit"
    },
    "close": {
      "type": "plain_text",
      "text": "Cancel"
    },
    "blocks": [
      {
        "type": "input",
        "block_id": "b-id",
        "label": {
          "type": "plain_text",
          "text": "Input label",
        },
        "element": {
          "action_id": "a-id",
          "type": "plain_text_input",
        }
      }
    ]
  }
)

See views.update for more info.

If you want to push a new view onto the modal instead of updating an existing view, reference the views.push documentation.


Emoji reactions

You can quickly respond to any message on Slack with an emoji reaction. Reactions can be used for any purpose: voting, checking off to-do items, showing excitement -— or just for fun.

This method adds a reaction (emoji) to an item (file, file comment, channel message, group message, or direct message). One of file, file_comment, or the combination of channel and timestamp must be specified.

response = client.reactions_add(
  channel="C0XXXXXXX",
  name="thumbsup",
  timestamp="1234567890.123456"
)

Removing an emoji reaction is basically the same format, but you’ll use reactions.remove instead of reactions.add

response = client.reactions_remove(
  channel="C0XXXXXXX",
  name="thumbsup",
  timestamp="1234567890.123456"
)

See reactions.add and reactions.remove for more info.


Listing public channels

At some point, you’ll want to find out what channels are available to your app. This is how you get that list.

response = client.conversations_list(types="public_channel")

Archived channels are included by default. You can exclude them by passing exclude_archived=1 to your request.

response = client.conversations_list(exclude_archived=1)

See conversations.list for more info.


Getting a channel’s info

Once you have the ID for a specific channel, you can fetch information about that channel.

response = client.conversations_info(channel="C0XXXXXXX")

See conversations.info for more info.


Joining a channel

Channels are the social hub of most Slack teams. Here’s how you hop into one:

response = client.conversations_join(channel="C0XXXXXXY")

If you are already in the channel, the response is slightly different. already_in_channel will be true, and a limited channel object will be returned. Bot users cannot join a channel on their own, they need to be invited by another user.

See conversations.join for more info.


Leaving a channel

Maybe you’ve finished up all the business you had in a channel, or maybe you joined one by accident. This is how you leave a channel.

response = client.conversations_leave(channel="C0XXXXXXX")

See conversations.leave for more info.


Listing team members

response = client.users_list()
users = response["members"]
user_ids = list(map(lambda u: u["id"], users))

See users.list for more info.


Uploading files

response = client.files_upload(
  channels="C3UKJTQAC",
  file="files.pdf",
  title="Test upload"
)

See files.upload for more info.


Calling any API methods

This library covers all the public endpoints as the methods in WebClient. That said, you may see a bit delay of the library release. When you’re in a hurry, you can directly use api_call method as below.

import os
from slack import WebClient

client = WebClient(token=os.environ['SLACK_API_TOKEN'])
response = client.api_call(
  api_method='chat.postMessage',
  json={'channel': '#random','text': "Hello world!"}
)
assert response["message"]["text"] == "Hello world!"

Web API Rate Limits

When posting messages to a channel, Slack allows applications to send no more than one message per channel per second. We allow bursts over that limit for short periods. However, if your app continues to exceed the limit over a longer period of time it will be rate limited. Different API methods have other rate limits – be sure to check the limits and test that your application has a graceful fallback if it should hit those limits.

If you go over these limits, Slack will start returning a HTTP 429 Too Many Requests error, a JSON object containing the number of calls you have been making, and a Retry-After header containing the number of seconds until you can retry.

Here’s a very basic example of how one might deal with rate limited requests.

import os
import time
from slack import WebClient
from slack.errors import SlackApiError

client = WebClient(token=os.environ["SLACK_API_TOKEN"])

# Simple wrapper for sending a Slack message
def send_slack_message(channel, message):
  return client.chat_postMessage(
    channel=channel,
    text=message
  )

# Make the API call and save results to `response`
channel = "#random"
message = "Hello, from Python!"
# Do until being rate limited
while True:
  try:
    response = send_slack_message(channel, message)
  except SlackApiError as e:
    if e.response["error"] == "ratelimited":
      # The `Retry-After` header will tell you how long to wait before retrying
      delay = int(e.response.headers['Retry-After'])
      print(f"Rate limited. Retrying in {delay} seconds")
      time.sleep(delay)
      response = send_slack_message(channel, message)
    else:
      # other errors
      raise e

See the documentation on Rate Limiting for more info.