blog/2020-03-24-2020-using-vyper-with-embark.md at 0dae3ea1a0f03f6c976ae2fd0a5562567d290d37

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title: Using Vyper with Embark summary: "Vyper has gained some traction on Solidity as an Ethereum smart contract language, especially with support going in to ETH2. Learn how to use Embark to use Vyper smart contracts in a ÐApp." author: eric_mastro categories:

Report layout: blog-post image: '/assets/images/vyper_simple_storage_with_logo.png'

Why Vyper?

Vyper is a contract-based approach to writing Ethereum smart contracts and is aimed at bringing "increased security and readability through a minimalist approach" to the smart contract landscape.

Although Vyper has gained some popularity in recent times as a security-focused alternative to Solidity, the simplicity required for such a case leaves out some features of Solidity that developers have come to appreciate.

In its current form, Vyper is python-based, but due to the Consensys audit highlighting some major security flaws, the Ethereum Foundation has decided to concurrently build a Rust-based Vyper, while community devs aim to support the original Python-based version.

{% notification danger 'Using Vyper in production' %} Because of the inherent security flaws, please do not use Python-based Vyper in production projects until the vyperlang team has created a production-ready release. Embark will also support Rust-based Vyper once it is released. {% endnotification %}

Irrespective of the security audit, Vyper is perhaps the most intuitive and easiest to quickly learn language for reading and writing Etheruem contracts - even without any prior knowledge or experience in programming. Additionally, Embark has created a plugin that makes it just as easy to compile Vyper contracts in an Embark ÐApp!

Let's see just how easy this is!

Prerequisites
Create a ÐApp
Install the Embark Vyper plugin
Add a Vyper contract to your ÐApp
Run Embark
Interact with your contract in Cockpit

Step 1. Prerequisites

Before we can write our first Vyper contract, let's take care of a few requirements.

Install Embark

Install Embark either globally or as a package in your ÐApp. The most simple way forward is to install Embark globally on your system:

yarn global add embark
# OR
npm i -g embark

The rest of this article will assume you have Embark installed globally, and therefore available from the CLI.

Install Vyper

If you haven't already done so, make sure to install Vyper. As the documentation recommends, be sure to use a Python virtual environment when installing Vyper, as it will keep your system-wide packages from being polluted.

Step 2. Create a ÐApp

For this article, we will be creating a demo ÐApp to use as a base for creating our first Vyper contract. However, if you already have a ÐApp that you'd like to add Vyper contracts to, simply skip this step.

Creating an Embark demo is easy, simply run the following commands:

embark demo
cd embark_demo

Step 3. Install the Embark Vyper plugin

Installing the Embark Vyper plugin in our ÐApp is extremely simple:

Add the embark-vyper package to your ÐApp:

yarn add embark-vyper
# OR
npm i embark-vyper --save

Add the embark-vyper plugin to embark.json:

// embark.json

// ...
"plugins": {
  "embark-ipfs": {},
  "embark-swarm": {},
  "embark-whisper-geth": {},
  "embark-geth": {},
  "embark-parity": {},
  "embark-profiler": {},
  "embark-graph": {},
  "embark-vyper": {} // <====== add this!
},
// ...

Step 4. Add a Vyper contract to your ÐApp

First, let's delete the SimpleStorage Solidity contract that comes with the Embark Demo by default:

rm contracts/simple_storage.sol

Next, let's create a Vyper contract in the contracts folder of our ÐApp, ie contract/SimpleStorage.vy (case is important):

# contracts/SimpleStorage.vy

storedData: public(int128)

@public
def __init__(_x: int128):
  self.storedData = _x

@public
def set(_x: int128):
  self.storedData = _x

The function of this contract is simple: upon creation (deployment), it will store the value we initially give it during deployment. We also have access to a set() that will allow to set the value stored in the contract.

Changing the contract filename

Because Vyper's constructor is called __init__, Embark must take the contract class name from the file name. If you'd prefer to change the name of your contract file to something else like contracts/simple_storage.vy, you'll need to update config/contract.js to allow Embark to match a contract configuration to a contract file:

// config/contracts.js

module.exports = {
  default: {
    // ...
    deploy: {
      simple_storage: { // NOTE: this only needs to be changed if the contract filename was changed
        fromIndex: 0,
        args: [100]
      }
    }
    // ...
  }
}

Please see the Embark smart contract configuration documentation for more information on how to configure contracts in Embark.

Step 5. Run Embark

Now that we have installed and configured everything, let's run Embark and watch the magic!

embark run --nodashboard --nobrowser

Assuming we kept the file name SimpleStorage.vy from step 4, we should see the following output in the console:

compiling Vyper contracts...
deploying contracts
Deploying SimpleStorage with 144379 gas at the price of 2000000000 Wei. Estimated cost: 288758000000000 Wei  (txHash: 0x370a864b12b1785b17180b2a10ec2f941a15638eeffadfecf5bbe68755a06f14)
SimpleStorage deployed at 0x5Baf4D88bC454537C51CEC7568a1E23400483abc using 135456 gas (txHash: 0x370a864b12b1785b17180b2a10ec2f941a15638eeffadfecf5bbe68755a06f14)

Troubleshooting

There are a few common issues you may experience when Embark attempts to compile and deploy your Vyper contracts.

Vyper is not installed on your machine

Vyper is not installed on your machine
You can install it by visiting: https://vyper.readthedocs.io/en/latest/installing-vyper.html

This means that the binary vyper cannot be found on your machine. If you're running *nix, you can verify this by running:

which vyper
# expected output: path/to/virtual-env/bin/vyper
# actual output: vyper not found

If vyper was installed in a virtual environment, you may have forgotten to activate the environment, ie:

source path/to/vyper-env/bin/activate

If vyper was not installed in a virual environment, it most likely means your PATH environment variable needs to be updated to point to the directory where the vyper binary is installed. You can inspect your PATH environment variable by:

echo $PATH

And update it with the path to the directory containing the vyper binary using:

export PATH=/path/to/vyper/dir:$PATH

Error deploying contract

SimpleStorage has no code associated
did you mean "simple_storage"?
deploying contracts
Error deploying contract simple_storage
[simple_storage]: Invalid number of parameters for "constructor". Got 0 expected 1!
Error deploying contracts. Please fix errors to continue.

This means that the contract simple_storage is a file in contracts/ and expected to be deployed by Embark, but is not configured for deploy in the contracts configuration. This could be the result of changing the filename of the Vyper contract to simple_storage.vy, but not updating the contracts configuration, as outlined in step 4.

Step 6. Interact with your contract in Cockpit

Given that the Vyper contract has the same functionality as the SimpleStorage.sol that ships with the default Embark demo, we could still run the Demo application and view that its functionality works as expected. However, an even easier approach to interacting with our deployed Vyper contract is to use Cockpit.

In your browser, open Cockpit using the link provided in the console, ie http://localhost:55555?token=<token from console> NOTE: the token parameter is provided in the Embark console once Embark has finished building pipeline files. This token can be copied to the clipboard by typing token in the console command prompt.

At the bottom, you should see your SimpleStorage contract. Click the name of the contract to open the interaction view:

Expand the set method interaction by clicking the set header. Enter a value to set the storedData variable in the contract to, ie 999:

Then click "Send". You should see the inputs and the resulting transaction hash:

Additionally, you should see the transaction printed in Embark's console:

Blockchain> SimpleStorage.set(999) | 0x71a9341fc8d52e53e11692b642b806a41da7aa8ed2b3ed6a975314639a131d32 | gas:26447 | blk:14 | status:0x1

Conclusion

Vyper is proving to be a useful language for writing secure smart contracts. While the latest security audit is looming, the EF is working on a Rust-based implementation that will hopefully propel Vyper towards its goals of being a security-centric, simplistic smart contract language.

In the meantime, we can use Embark to write and deploy our Vyper contracts using the Embark Vyper plugin.

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