Async Gas Price Strategy

[UB18Aux]

What happened?

I'm using an async node and set the gas price strategy to the default fast_gas_price_strategy. This yields a TypeError: 'coroutine' object is not subscriptable.

Code that produced the error

node_async.eth.set_gas_price_strategy(web3.gas_strategies.time_based.fast_gas_price_strategy)
[...]
parameters = {"chainId" : ..., "from": ..., etc}
tx = await my_contract.functions.my_function().build_transaction(parameters)

Full error output

File "[....]/Executor.py", line 92, in [....]
    tx = await my_contract.functions.my_function().build_transaction(parameters)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[....]/.venv/lib/python3.12/site-packages/web3/contract/async_contract.py", line 360, in build_transaction
    return await async_build_transaction_for_function(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[....]/.venv/lib/python3.12/site-packages/web3/contract/utils.py", line 444, in async_build_transaction_for_function
    return await async_fill_transaction_defaults(async_w3, prepared_transaction)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[....]/.venv/lib/python3.12/site-packages/web3/_utils/async_transactions.py", line 115, in async_fill_transaction_defaults
    strategy_based_gas_price = async_w3.eth.generate_gas_price(transaction)
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[....]/.venv/lib/python3.12/site-packages/web3/eth/base_eth.py", line 88, in generate_gas_price
    return self._gas_price_strategy(self.w3, transaction_params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[....]/.venv/lib/python3.12/site-packages/web3/gas_strategies/time_based.py", line 220, in time_based_gas_price_strategy
    if w3.eth.get_block("latest")["number"] == 0:
       ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
TypeError: 'coroutine' object is not subscriptable

Fill this section in if you know how this could or should be fixed

Change time_based_gas_price_strategy to check if w3 node is async or not.

web3 Version

6.20.0

Python Version

3.12.3

Operating System

ubuntu 24

Output from pip freeze

No response

[fselmo]

Seeing as a lot of layer 2 transactions still rely on gasPrice, I think this is a simple enough task still relevant to Ethereum. It's hard to measure how much use these older middleware are getting, and Ethereum moving to EIP-1559 fees sort of put the async-ing of these to the side. I'd review a PR for this if it was submitted though, otherwise I think it'll have to wait a bit until we are freed up with other tasks. Thanks for submitting.