Python SDK

Prerequisite: Sign up for an EthVigil developer account

To use the EthVigil Python SDK, you need to be signed up for a beta developer account on https://beta.ethvigil.com

You can choose any of the following approaches.

Sign up via the CLI tool ev-cli (Recommended )

Follow the instructions sequentially from these steps detailed in the links below.

This approach allows you to have control on your EthVigil developer account from your command line itself without having to switch to the Web UI.

Once you have completed this section, head to Quickstart.

Sign up on the web UI

Once you have signed up on the web UI

  • you have to manually export your settings from the dashboard
  • To copy the downloaded file into ~/.ethvigil/settings.json run the following commands in your terminal
cd ~
mkdir .ethvigil
# export key downloads a settings.json file into the Downloads directory
cp ~/Downloads/settings.json ~/.ethvigil/settings.json

Note: The ~ in the above file path denotes your home directory on Linux/MacOS

Quickstart

Install EthVigil Python SDK

Choose any of the following approaches.

Either of them should install a python module ethvigil

  1. pip install from Github repo

pip install git+https://github.com/blockvigil/ethvigil-python-sdk.git

  1. Do a local pip install after git clone

git clone https://github.com/blockvigil/ethvigil-python-sdk.git
pip install ethvigil-python-sdk/

Test import

Launch python in interactive mode and test if you can import the module. if you do not see any ImportError or other exceptions, you would want to move on to exploring the SDK further.

python
Python 3.6.5 (default, Jul 31 2019, 23:25:49)
[GCC 4.2.1 Compatible Apple LLVM 10.0.1 (clang-1001.0.46.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from ethvigil.EVCore import EVCore
>>>

Initialize EthVigil API instance

You can find the following usage examples in the examples/ directory as well.

EVCore

from ethvigil.EVCore import EVCore
evc = EVCore(verbose=False)

If you configure the logging module appropriately, passing verbose=True to the above initialization will begin printing debug information on to the console.

Here is an example:

>>> import logging
>>> import sys
>>> stdout_handler = logging.StreamHandler(sys.stdout)
>>> stdout_handler.setLevel(logging.DEBUG)
>>> logging.getLogger('EVCore').level = logging.DEBUG
>>> logging.getLogger('EVCore').addHandler(stdout_handler)
>>> from ethvigil.EVCore import EVCore
>>> e = EVCore(verbose=True)

Deploy a contract

Find the microblog.sol Solidity smart contract in the examples directory of the SDK github repo.

from ethvigil.EVCore import EVCore
evc = EVCore(verbose=False)
r = evc.deploy(
contract_file='microblog.sol',
contract_name='Microblog',
inputs={
'_ownerName': 'anomit',
'_blogTitle': 'TheBlog'
}
)
print(r['contract'])

The contract will be deployed at the address displayed above.

Accessing previously deployed contracts

You can access operations on a contract previously deployed through EthVigil by calling the generate_contract_sdk() function on the EVCore instance.

from ethvigil.EVCore import EVCore
evc = EVCore(verbose=False)
# put in a contract address deployed from your EthVigil account
contract_instance = evc.generate_contract_sdk(
contract_address='0xContractAddress',
app_name='microblog'
)

All the functions defined in the Solidity smart contract can be accessed by the same names against this contract instance. Read on to find out how.

Reading from a contract

We will be using the contract instance from the above example.

# calling the owner() function on the contract.
# This is a 'read' call, does not change state of the contract
print(contract_instance.blogTitle())

Example source code: examples/contract_read.py

Writing to a contract

Changing the microblog title

# calling the changeBlogTitle() function on the contract.
# This is a 'write' call, hence it changes state of the contract
# you can pass the arguments expected by the function as keyword parameters
# this sends out a transaction on the network
print(contract_instance.changeBlogTitle(_blogTitle='NewTitle'))

Example source code: examples/contract_write_changeBlogTitle.py

Adding a new post

# -- expanding keyword params from a mapping --
print(contract_instance.addPost(**{
'title': 'New2',
'body': 'Body2',
'url': 'foo_url',
'photo': 'http://imgurl/baz_photo'
}))

Example source code: examples/contract_write_addPost.py

Transactions that change the state of a smart contract take anywhere between 5-15 seconds to get confirmed on the blockchain.

This makes it necessary to build an asynchronous pattern for your blockchain applications. Let us take a look at it in the next section.

Webhook integrations: Receive JSON payloads from events and other contract activity

EthVigil does the hard work of monitoring your contracts, transactions on them and events that may be emitted by transactions triggering certain logic.

You can use these updates to enhance your blockchain applications and execute further logic "off-chain". Connect to multiple services like recording a new entry on Airtable, create a new Google Doc, executing IFTTT recipes; the possibilities are literally endless.

Step 1: Set up a publicly available URL to which EthVigil can push these updates.

For this example, we shall use ngrok to setup a publicly available URL in the format https://<randomstring>.ngrok.com . The tool receives HTTP payloads on this public URL and forwards them to a local HTTP server (running on your computer).

ngrok HTTP tunneling Image Credit: Ngrok.com

Technically this is known as HTTP tunnelling but let's not worry about semantics right now.

Follow the instructions on ngrok.com to install and setup the tool.

Then run it on the terminal with the following command.

./ngrok http 8044

This will forward HTTP requests to a local server running on port 8044. In the next step, we fire up this local server.

Step 2: Run the local HTTP server

We have included the code for this in examples/sample_webhook_listener.py. Open a new tab/window in your terminal and run it

python sample_webhook_listener.py

This starts a tornado server running on port 8044. The example code logs every received payload on the terminal.

Step 3: Register the public ngrok URL with EthVigil to receive updates

Example code: examples/webhook_integrations.py

Copy the https URL against the Forwarding information from the running ngrok console. It will look something like this:

from ethvigil.EVCore import *
evc = EVCore(verbose=False)
# put in a contract address deployed from your EthVigil account
contract_instance = evc.generate_contract_sdk(
contract_address='0xContractAddress',
app_name='microblog'
)
# the URL to which event updates on the smart contract will be delivered by EthVigil
callback_url = 'https://f6192ec6.ngrok.io'
# EthVigil will watch over 'NewPost' event updates.
# Events to be monitored are specified as a list of event names
print(contract_instance.add_event_integration(events=['NewPost'], callback_url=callback_url))

Continuing from the microblog.sol example, let us attempt to receive an update the NewPost event that is emitted when you call addPost() on the contract instance.

Step 4: Call addPost() and observe the local HTTP server

Apart from the terminal where ngrok is running, open up two more new terminal tabs or windows.

from ethvigil.EVCore import EVCore
evc = EVCore(verbose=False)
# put in a contract address deployed from your EthVigil account
contract_instance = evc.generate_contract_sdk(
contract_address='0x6862aa9d817882e617206203c3442e625a202fce',
app_name='microblog'
)
print(contract_instance.addPost(**{'title': 'NewPost1', 'body': 'This is just a string', 'url': 'not applicable', 'photo': 'not applicable'}))

This should generate a transaction to the contract. Shift to the terminal where sample_webhook_listener.py is running.

You should see the NewPost event being delivered to the script.

GIF demonstrating the process of adding webhook integration

EthVigil Python SDK Webhook Integration

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