Easier way to check if a piece of middleware is already added

[antazoey]

• Version: 6.8.0
• Python: 3.10
• OS: macos
• pip freeze output

not super relevant and really big and full of the weirdest stuff, please dont make me

What was wrong?

OK, right now if you try to add middleware that already exists, youll hit this line: https://github.com/ethereum/web3.py/blob/main/web3/datastructures.py#L174

            if name is element:
                raise ValueError("You can't add the same un-named instance twice")

and one way to handle this downstream is like this:

            try:
                self.web3.middleware_onion.inject(geth_poa_middleware, layer=0)
            except ValueError as err:
                if "You can't add the same un-named instance twice" in str(err):
                    # Already added
                    pass
                else:
                    raise  # Original error

but it doesn't seem very reliable and try/except is always a last-resort.

How can it be fixed?

Add a method, perhaps __contains__, that allows me to only add middleware if it is not already added.
I'd like to write it like this:

if geth_poa_middleware not in self.web3.middleware_onion:
    self.web3.middleware_onion.inject(geth_poa_middleware, layer=0)

Alternatively, a custom error would work:

try:
    self.web3.middleware_onion.inject(geth_poa_middleware, layer=0)
except MiddlewareAlreadyAddedError:
    pass  # Is ok

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[antazoey]

dang, it is there! oops not sure what i was doing wrong

[fselmo]

@antazoey no worries. Glad you got it working 👍🏼