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PY: Vote On Content

How to vote on a post/comment using Python.

Full, runnable src of Vote On Content can be downloaded as part of: tutorials/python (or download just this tutorial: devportal-master-tutorials-python-17_vote_on_content.zip).

In this tutorial we will explain and show you how to to check if a user has voted on specified content and also how to submit a vote on the Hive blockchain using the beem library.

Intro

Voting is a way of promoting good content via an upvote or reporting misuse, spam or other unfit content by downvoting. The Hive python library has a built-in function to transmit transactions to the blockchain. We are using the vote method found within the commit class in the the library. Before we vote on content we first check whether the user has already voted. This is not strictly necessary as a voting operation overrides the previous vote value. We use the get_active_votes function to check for this. This function only requires two parameters, the author and the permlink for the comment/post that the query is for. This returns a list of the current voters for that comment. The vote function has 3 parameters:

  1. identifier - This is a combination of the author and permink of the post/comment that the vote will be on
  2. weight - This value determines whether the vote is an upvote (+100.0), a downvote (-100.0), or zero (0) to remove previous vote.
  3. username - The name of the account that is executing the vote

Steps

  1. App setup - Library install and import. Connection to testnet
  2. User information - Input user information and connection to Hive node
  3. Check vote status - Vote status of post/comment
  4. Commit vote - Commit vote to the blockchain

1. App setup

In this tutorial we use 3 packages:

We import the libraries and connect to the testnet.

from pick import pick
import getpass
from beem import Hive
from beem.account import Account
from beem.vote import ActiveVotes
from beem.transactionbuilder import TransactionBuilder
from beembase.operations import Vote

Because this tutorial alters the blockchain we connect to the testnet so we don’t create spam on the production server.

2. User information

We also require the private posting key of the user that wishes to vote on the selected content so the action can be committed to the blockchain. This is why we have to specify this along with the testnet node. The values are supplied via the terminal/console before we initialise the beem class. We have supplied a test account, cdemo to use with this tutorial but any account set up on the testnet can be used.

# capture user information
voter = input('Please enter your username (voter): ')

# connect node
# If using mainnet, try with demo account: cdemo, posting key: 5JEZ1EiUjFKfsKP32b15Y7jybjvHQPhnvCYZ9BW62H1LDUnMvHz
client = Hive('http://127.0.0.1:8090')

3. Check vote status

In order to give the user an educated choice we first check whether they have already voted on the given post/comment. The author and permlink for the post is supplied via the console/terminal.

# capture variables
author = input('Author of post/comment that you wish to vote for: ')
permlink = input('Permlink of the post/comment you wish to vote for: ')

The vote status check is done with a simple query to the blockchain.

# check vote status
# noinspection PyInterpreter
print('checking vote status - getting current post votes')
identifier = ('@' + author + '/' + permlink)
author_account = Account(author)
result = ActiveVotes(identifier)
print(len(result), ' votes retrieved')

This query returns a list of the current voters on the specified post/comment. The result is checked against the username to determine what the current status is.

if result:
  for vote in result :
    if vote['voter'] == voter:
      title = "This post/comment has already been voted for"
      break
    else:
      title = "No vote for this post/comment has been submitted"
else:
  title = "No vote for this post/comment has been submitted"

4. Commit vote

The result from the previous step is used to give the user a choice in what the next step in the operation should be.

# option to continue
options = ['Add/Change vote', 'Cancel without voting']
option, index = pick(options, title)

The user is given a choice to either continue with the vote or cancel the operation. If the user elects to continue, the vote function is executed. The weight of the vote is input from the UI and the identifier parameter is created by combining the author and permlink values.

if option == 'Add/Change vote':
  weight = input('\n' + 'Please advise weight of vote between -100.0 and 100 (zero removes previous vote): ')
  try:
    tx = TransactionBuilder(blockchain_instance=client)
    tx.appendOps(Vote(**{
      "voter": voter,
      "author": author,
      "permlink": permlink,
      "weight": int(float(weight) * 100)
    }))

    wif_posting_key = getpass.getpass('Posting Key: ')
    tx.appendWif(wif_posting_key)
    signed_tx = tx.sign()
    broadcast_tx = tx.broadcast(trx_id=True)

    print("Vote cast successfully: " + str(broadcast_tx))
  except Exception as e:
    print('\n' + str(e) + '\nException encountered.  Unable to vote')

else:
  print('Voting has been cancelled')

When the function is executed the selected vote weight overrides any value previously recorded on the blockchain.

A simple confirmation of the chosen action is printed on the screen.

To Run the tutorial

Before running this tutorial, launch your local testnet, with port 8090 mapped locally to the docker container:

docker run -d -p 8090:8090 inertia/tintoy:latest

For details on running a local testnet, see: Setting Up a Testnet

  1. review dev requirements
  2. git clone https://gitlab.syncad.com/hive/devportal.git
  3. cd devportal/tutorials/python/17_vote_on_content
  4. pip install -r requirements.txt
  5. python index.py
  6. After a few moments, you should see a prompt for input in terminal screen.