Gas Price API

For Ethereum transactions, gas price is a delicate property. For this reason, Web3 includes an API for configuring it.

By default, Web3 will not include a gasPrice in the transaction as to relay this responsibility to the connected node. The Gas Price API allows you to define Web3’s behaviour for populating the gas price. This is done using a “Gas Price Strategy” - a method which takes the Web3 object and a transaction dictionary and returns a gas price (denominated in wei).

Retrieving gas price

To retreive the gas price using the selected strategy simply call generateGasPrice()

>>> Web3.eth.generateGasPrice()
20000000000

Creating a gas price strategy

A gas price strategy is implemented as a python method with the following signature:

def gas_price_strategy(web3, transaction_params=None):
...

The method must return a positive integer representing the gas price in wei.

To demonstrate, here is a rudimentary example of a gas price strategy that returns a higher gas price when the value of the transaction is higher than 1 Ether.

from web3 import Web3

def value_based_gas_price_strategy(web3, transaction_params):
    if transaction_params['value'] > Web3.toWei(1, 'ether'):
        return Web3.toWei(20, 'gwei')
    else:
        return Web3.toWei(5, 'gwei')

Selecting the gas price strategy

The gas price strategy can be set by calling setGasPriceStrategy().

from web3 import Web3

def value_based_gas_price_strategy(web3, transaction_params):
    ...

w3 = Web3(...)
w3.eth.setGasPriceStrategy(value_based_gas_price_strategy)

Available gas price strategies

web3.gas_strategies.rpc.rpc_gas_price_strategy(web3, transaction_params=None)

Makes a call to the JSON-RPC eth_gasPrice method which returns the gas price configured by the connected Ethereum node.

web3.gas_strategies.time_based.construct_time_based_gas_price_strategy(max_wait_seconds, sample_size, probability)

Constructs a strategy which will compute a gas price such that the transaction will be mined within a number of seconds defined by max_wait_seconds with a probability defined by probability. The gas price is computed by sampling sample_size of the most recently mined blocks.

  • max_wait_seconds The desired maxiumum number of seconds the transaction should take to mine.
  • sample_size The number of recent blocks to sample
  • probability An integer representation of the desired probability that the transaction will be mined within max_wait_seconds. 0 means 0% and 100 means 100%.

The following ready to use versions of this strategy are available.

  • web3.gas_strategies.time_based.fast_gas_price_strategy: Transaction mined within 60 seconds.
  • web3.gas_strategies.time_based.medium_gas_price_strategy: Transaction mined within 5 minutes.
  • web3.gas_strategies.time_based.slow_gas_price_strategy: Transaction mined within 1 hour.
  • web3.gas_strategies.time_based.glacial_gas_price_strategy: Transaction mined within 24 hours.

Warning

Due to the overhead of sampling the recent blocks it is recommended that a caching solution be used to reduce the amount of chain data that needs to be re-fetched for each request.

from web3 import Web3, middleware
from web3.gas_strategies.time_based import medium_gas_price_strategy

w3 = Web3()
w3.eth.setGasPriceStrategy(medium_gas_price_strategy)

w3.middleware_onion.add(middleware.time_based_cache_middleware)
w3.middleware_onion.add(middleware.latest_block_based_cache_middleware)
w3.middleware_onion.add(middleware.simple_cache_middleware)