← Guides / Web3 SDKs / Estimating gas price using pending transactions in Python

June 08, 2021

Estimating gas price using pending transactions in Python

Overview

To send a transaction on the Ethereum network, you need to pay fees for including the transaction in a block as well as the computation necessary in the transaction; this fee is called gas. The transactions are accepted into the block based on the amount of gas they are sent with, so being able to see current gas prices is an advantageous ability. This guide will cover estimating gas prices using pending transactions in Python using the Web3Py library.

Prerequisites

Python installed in your system (version 3.6+) and Pip3.
A text editor.

What is gas in Ethereum?

Gas is the unit to measure the amount of computational effort required to do a particular operation. Most smart contracts running on EVMs (Ethereum Virtual machines) are written in Solidity. Each line of code or every Solidity function requires gas to be executed.

The following image is taken from Ethereum Yellow Paper. It gives a rough idea of how much gas a specific instruction can cost.

So, gas fees are payments made by the users to compensate the computing energy of the Ethereum network used while making their transactions. To draw an analogy, to drive a car for a certain distance A requires a certain amount of gas/fuel B. Similarly, sending a certain amount of ETH or sending a smart contract A requires a certain amount of fee (gas) B.

Requiring a gas fee also prevents the Ethereum network from abusive practices such as spamming the network. It also encourages the developers to make code more efficient to avoid expensive computational operations and infinite loops.

Gas is measured in Gwei (short for GigaWei) - it is a subunit of the currency Ether (ETH) used on the Ethereum network (1,000,000,000 Gwei = 1 ETH). Having a separate unit helps differentiate between the currency ETH valuation and the computational cost of using EVM.

Why estimate gas?

Why do we want to estimate gas? Well as it stands today, miners choose which transactions to mine into blocks. How do miners choose which transactions to put into a block? They tend to pick the transactions that include the most gas. Why do they pick the transactions with the most gas? Because miners get to keep the gas fees included with a transaction. Transactions with gas lower than the current average gas typically take a long time to get verified or even dropped by miners in the worst-case scenario.

So if we pay a lot of gas, we get our transaction included. If we don’t pay enough gas, our transaction could get dropped. But how much gas to pay to incentivize miners? That’s where gas estimation comes in.

To make more sense of estimating gas and gas prices, let’s put some formal definitions behind them:

Gas: The unit to measure the computational cost of a particular action executed on EVM. For example - I can include 25,000 gas to complete some transaction.

Gas Limit: The maximum amount of gas a user is willing to pay for that action to get executed (a minimum of 21,000).

Gas Price: Amount of Gwei a user is willing to spend on each gas unit.

We want to figure out what gas price is average, then include a slightly higher gas price for our transactions. We don’t really care about the gas limit or gas sent; as long as they’re high enough, we’ll get refunded whatever gas was not used.

Now, let's try to estimate the gas for a simple ETH transfer transaction. Let's get the actual estimate of gas by looking at the pending transactions.

Installing Web3.py

Our first step here would be to check if Python 3.6 or higher is installed on your system; you can check if Python is installed on not by typing the following in your terminal/cmd:

$ python --version

If not installed, you can follow the instructions on the Downloads page of Python’s official website.

We’ll use Web3.py, a Python library used to interact with Ethereum. We’ll install Web3.py using PIP. Type the following in your terminal/cmd:

$ pip install web3

Note: Python and other library versions cause common installation problems. Therefore, if you face any problems, try setting up a virtual environment and troubleshoot the web3.py installation.

If everything goes right, Web3.py will be installed in your system. If you’d like to check out some other things Web3.py can do, check out our guides on how to connect to Ethereum using Web3.py and generating a new Ethereum address using Web3.py.

Booting our Ethereum node

For our purposes today, we could use pretty much any Ethereum client with mempool support, such as Geth or OpenEthereum (fka Parity). Since that is a bit too involved for just estimating gas, we'll just grab a free endpoint from QuickNode to make this easy. After you've created your free ethereum endpoint, copy your HTTP Provider endpoint:

You'll need this later, so copy it and save it.

Estimating Gas

The first thing we’re going to do is a simple estimation of the number of gas to send a transaction. Create a python file named gas.py and copy-paste the following code into it. This is an estimategas example for ETH transfer transaction.

from web3 import Web3, HTTPProvider
web3 = Web3(HTTPProvider("ADD_YOUR_ETHEREUM_NODE_URL"))
estimate = web3.eth.estimateGas({'to': '0xd3CdA913deB6f67967B99D67aCDFa1712C293601', 'from': '0x6E0d01A76C3Cf4288372a29124A26D4353EE51BE', 'value': 145})
print("Gas estimate is: ", estimate)

So go ahead and replace `ADD_YOUR_ETHEREUM_NODE_URL` with the http provider from the section above.

Explanation of the code above:

Line 1: Importing web3 and HTTPProvider.

Line 2: Setting our node URL.

Line 3: Estimating gas using estimateGas function for an ETH transfer transaction.

Line 4: Printing the estimate.

Now, run your Python script using.

$ python gas.py

It should look like this.

The above example estimate does not actually tell us what gas price we should pay for the transaction. Let’s get a measure of what gas price we should be willing to pay by looking at the pending transactions from our Ethereum node.

Create a Python file named gas_pt.py and copy-paste the following code into it.

from web3 import Web3, HTTPProvider
import statistics
web3 = Web3(HTTPProvider("ADD_YOUR_ETHEREUM_NODE_URL"))
pending_transactions = web3.provider.make_request("parity_pendingTransactions", [])
gas_prices = []
gases = []
for tx in pending_transactions["result"[:10]]:
	gas_prices.append(int((tx["gasPrice"]),16))
	gases.append(int((tx["gas"]),16))

print("Average:")
print("-"*80)
print("gasPrice: ", statistics.mean(gas_prices))
print(" ")
print("Median:")
print("-"*80)
print("gasPrice: ", statistics.median(gas_prices))

So go ahead and replace `ADD_YOUR_ETHEREUM_NODE_URL` with the http provider from the section above.

Explanation of the code above:

Line 1: Importing web3 and HTTPProvider.

Line 2: Importing Statistics package.

Line 3: Setting our node URL

Line 4: Getting pending transactions and storing them into an array and then to pending_transactions variable.

Line 5-6: Creating gas_prices and gases arrays.

Line 7-9: Getting the first ten elements (transactions) of the results array from pending_transactions and appending the values of gasPrice to gas_prices array after converting them to decimal from hexadecimal, appending the values of gas to gases array after converting them to decimal from hexadecimal.

Line 11-12: Printing the string “Averages:” and 80 dashes for clean output.

Line 13: Printing average gas price with string “gasPrice:” by getting mean of the gasPrice values stored in gas_prices array.

Line 14: Printing a space.

Line 15-16: Printing the string “Median:” and 80 dashes for clean output.

Line 17: Printing median gas price with string “gasPrice:” by getting median of the gasPrice values stored in gas_prices array.

Now, run the Python script.

$ python gas_pt.py

If the code gets executed successfully, it should look something like this. It may take a while for the code to get entirely executed as it has first to get the pending transactions (which can be a lot) and then query them.

You can see the average and median gas and gas prices in the above image.

Conclusion

Now you know how to estimate gas and gas prices, make sure to Estimate gas costs before sendTransaction function or Estimate the cost for deploying smart contracts. Check out an example of re-sending a transaction with a higher gas value using JavaScript.

Subscribe to our newsletter for more articles and guides on Ethereum. If you have any feedback, feel free to reach out to us via Twitter. You can always chat with us on our Discord community server, featuring some of the coolest developers you’ll ever meet :)

Ready to try QuickNode? Start your 7-day free trial

Overview
What is gas in Ethereum?
Why estimate gas?
Installing Web3.py
Booting our Ethereum node
Estimating Gas
Conclusion

Sahil Sen

Web developer who believes in power of communities and is passionate about community building. Developer evangelist @ QuickNode.

Want more Web3 tuts?

We'll send you the latest tech and tutorials via our weekly Web3 Vibes newsletter.

Related articles 27

Jul 3, 2021 The Web3 Developer Stack

A developer stack is a bag of technologies a developer possesses. For example, MEAN (MongoDB, Express.js, AngularJS/Angular, and Node.js) and MERN (MongoDB, Express.js, React, and Node.js) are common web developer stacks. Similarly, today we will learn more about the web3...

Jun 7, 2021 How to integrate IPFS with Ethereum

It can be costly to store massive files on a blockchain mainnet, and this is where decentralized file storing systems like IPFS can come in handy. Sometimes, NFTs use IPFS as well. In this guide, we’ll cover how we can integrate IPFS with...

Jun 8, 2021 How to generate a new Ethereum address in PHP

PHP is very popular in developing the backend of websites or web applications. PHP has a huge crowd of developers trusting it as their go-to language. In this guide, we will see how we can generate a new Ethereum address in...

Jun 8, 2021 How to connect to Ethereum network with ethers.js

When someone thinks of developing a dApp the first tool that comes to their mind is web3.js which is pretty common because of its popularity in the community and wide use cases, dApp development has been consistently growing and there are a lot of developers who want to...

Jun 8, 2021 How to connect to the Ethereum network using Ruby

Ruby has a huge fanbase. Ruby was developed by its creator with an intention to create a language people can have fun using. Ruby has been largely accepted by the developers all around the world since it’s launch, in fact, the biggest tech communities in many cities are...

Jun 8, 2021 How to re-send a transaction with higher gas price using ethers.js

Sometimes, you submit a transaction on Ethereum without enough gas due to network congestion or too many pending transactions offering a higher gas price than you have offered on your transaction. If you have a high priority transaction but low gas, you could end up...

Jun 17, 2021 How to get the balance of an ERC-20 token

When a new token is made on the Ethereum network, it usually follows a specification. The most popular of which is the ERC20 specification. To meet this ERC20 standard, one's token must have a multitude of...

Jun 8, 2021 How to connect to Ethereum network with Web3.js

Libraries and frameworks make the development process a lot easier and faster. When it comes to Ethereum development, Web3.js is the go to library. That's because Web3.js is the official library, from the

Jun 8, 2021 How to generate a new Ethereum address in Ruby

With high usage in web applications and straightforward syntax, Ruby is used by a vast number of people. This guide will cover creating an Ethereum address in Ruby using ruby-eth...

Jun 8, 2021 How to Fork Ethereum Blockchain with Ganache.

Forking and running a local simulated Ethereum environment is essential if you want to work with DeFi or do Ethereum development in general. In this guide, we’ll cover how to fork Ethereum Blockchain with

Jun 8, 2021 How to fetch Ethereum event logs in Ruby

Ethereum log records are very useful to understand and keep track of smart contract events. In this guide, we are going to learn how to fetch ethereum event logs in Ruby using ethereum.rb ruby...

Jun 9, 2021 How to generate a new Ethereum address in Go

Golang is very popular among backend developers for building infrastructures and microservices. Go is a procedural programming language. Developed in 2007 by Robert Griesemer, Rob Pike, and Ken Thompson at Google, then launched in 2009 as...

Jun 9, 2021 How to generate a new Ethereum address in Python

Python is one of the most versatile programming languages out there with an abundance of use cases; We can build many applications with Python from client-side to back end. In this guide, we will cover creating an Ethereum address in Python using the

Jun 9, 2021 How to generate a new Ethereum address in JavaScript

When it comes to programming, there’s hardly anyone who has not used or heard about JavaScript. JavaScript was initially created for client-side scripting but has become a full-featured Object-Oriented...

Jun 9, 2021 How to connect to Ethereum network using Go

Go helps you make faster scalable backends and this guide will show you how to connect your backend to Ethereum (and make it even faster, more reliable, and globally accessible, all thanks to QuickNode’s global infrastructure). What is...

Jun 9, 2021 How to connect to Ethereum network using Java / Web3j

We can say that Java is one of the most versatile languages out there, and it continues to be relevant in today's time. Java is so popular because of its massive user base and use cases. In this guide/tutorial, we'll learn how to connect to the Ethereum Blockchain network...

Jul 25, 2021 How to Create an Address in Solana using JavaScript

Hello reader! Welcome to QuickNode's first Solana guide. Solana is an up-and-coming blockchain that seeks to solve the scalability issues that Ethereum has been handling. You will walk through step-by-step how to create a Solana address using the @solana/web3.js...

Jun 9, 2021 How to connect to Ethereum using .NET (Nethereum)

Dotnet or .NET is very popular for the development of desktop applications, most Windows desktop applications are built using .NET, and it also contributes largely to web application’s tech stack. In this guide, let’s see how we can connect to Ethereum using .NET and

Jun 15, 2021 How to connect to Ethereum using PHP

PHP is a very popular choice among developers and has a vast community due to its long presence in web development. In this guide, we’ll cover how to connect to Ethereum with PHP using the web3.php...

Jul 15, 2021 How to Setup Local Development Environment for Solidity

The success story of blockchain started with Bitcoin and was given wings by Ethereum. Ethereum was the first blockchain to introduce programmable software to the immutable ledger; these programs that live on the blockchain are called smart contracts. Solidity is the...

Jun 9, 2021 How to use Subspace with QuickNode

In this guide, we'll understand a bit about reactive development and how to use Subspace with QuickNode.JavaScript is the programming language behind most of the internet apps and websites. JavaScript today has become one of the most used programming languages,...

Jun 9, 2021 How to connect to the Ethereum network using Python using Web3.py

You can build Ethereum applications in different programming languages. In this article, we will connect to the Ethereum network using Python.PrerequisiteEthereum Node (We will use QuickNode’s free...

Jul 24, 2021 How to deploy a smart contract with Brownie

Python is one of the most versatile programming languages; from researchers running their test models to developers using it in heavy production environments, it has use cases in every possible technical field. In today's guide, we will learn about Brownie, a Python-based...

Jul 13, 2021 How To Fork Ethereum Mainnet with Hardhat

Forking the chain at an older block of the blockchain is helpful if you want to simulate the blockchain’s state at that block; Hardhat has this functionality built in. In this guide, let’s go through the process of forking the Ethereum Mainnet at an older...

Jun 26, 2021 How to create and deploy a smart contract with Hardhat

Ethereum development environments like Truffle and Hardhat make it easier to work with smart contracts and Ethereum nodes. They provide a set of tools to seamlessly write, test, and deploy...

Jul 2, 2021 How to do a non-custodial transaction with QuickNode

Private keys are one of the most sensitive pieces of data when it comes to cryptography, cryptocurrencies, and blockchain. However, there has always been debate/confusion about choosing between custodial wallets (where the wallet provider has custody of the user’s private...

Jul 2, 2021 How to generate a new Bitcoin address in JavaScript

To do any type of transaction on the Bitcoin blockchain, you’ll need a public key or a Bitcoin address. In this guide, we’ll cover how to generate a new Bitcoin address in JavaScript using CyrptoCoinJS.