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
>>> web3.eth.generate_gas_price() 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
from web3 import Web3 def value_based_gas_price_strategy(web3, transaction_params): ... w3 = Web3(...) w3.eth.set_gas_price_strategy(value_based_gas_price_strategy)
Available gas price strategies¶
Makes a call to the JSON-RPC eth_gasPrice method which returns the gas price configured by the connected Ethereum node.
construct_time_based_gas_price_strategy(max_wait_seconds, sample_size=120, probability=98, weighted=False)¶
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_secondswith a probability defined by
probability. The gas price is computed by sampling
sample_sizeof the most recently mined blocks. If
weighted=True, the block time will be weighted towards more recently mined blocks.
max_wait_secondsThe desired maxiumum number of seconds the transaction should take to mine.
sample_sizeThe number of recent blocks to sample
probabilityAn 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.
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.set_gas_price_strategy(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)