How to use web3.py to connect to non-mainnet ENS?

Question

This github issue on web3.py is "Document how to set up ENS for non-mainnet addresses."

This question (that I filed) is me thrashing around trying to do so.

How do you set up ENS for non-mainnet addresses? For example, Rinkeby?

Answer 1

Got an answer. You have to inject some middleware at exactly the right spot.

from web3 import Web3
from web3.auto.infura import (
    INFURA_MAINNET_DOMAIN, build_http_headers, build_infura_url)
from web3.auto.infura.endpoints import INFURA_RINKEBY_DOMAIN
from web3.providers.auto import load_provider_from_uri

from ens import ENS
from eth_typing import ChecksumAddress

_headers = build_http_headers()

# NOTE: build_infura_url requires WEB3_INFURA_PROJECT_ID
# and WEB3_INFURA_API_SECRET environment variables set.
if False:
    # Works with mainnet
    _infura_url = build_infura_url(INFURA_MAINNET_DOMAIN)
else:
    # Doesn't work with Rinkeby
    #
    # "web3.exceptions.ExtraDataLengthError: The field extraData is 97 bytes,
    #  but should be 32. It is quite likely that you are connected to a POA chain.
    #  Refer to http://web3py.readthedocs.io/en/stable/middleware.html#geth-style-proof-of-authority
    #  for more details."
    _infura_url = build_infura_url(INFURA_RINKEBY_DOMAIN)

w3 = Web3(load_provider_from_uri(_infura_url, _headers))
ens = ENS.fromWeb3(w3)

from web3.middleware import geth_poa_middleware
# NOTE: have to inject this into ens.web3, not w3
ens.web3.middleware_onion.inject(geth_poa_middleware, layer=0)

the_ens = ens.name(
    ChecksumAddress('0x5B2063246F2191f18F2675ceDB8b28102e957458'))
print(the_ens)  # Returns None, presumably not mapped on Rinkeby
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