Signing a PSBT with some inputs not having utxo throws ValueError

[AdamISZ]

I was previously using sign() method of psbt.PartiallySignedTransaction with a keystore containing keys for only some inputs, and it was working fine, but I now have a use case where some of the other inputs (which I'm not signing and don't have keys for) are required (see BIP78) to not have the utxo field filled in. When I call sign() in this case, those inputs throw the above mentioned ValueError (which btw has a trivial typo: 'utxo is not set for of PSBT_Input at index {self.index}').

Currently I only have the ugly option of signing first, then deleting the utxo field. But unless I missed something, it should be possible to call sign() on the overall PSBT without it throwing an Exception (though I suppose, it could certainly be an option).

[dgpv]

Yes, it looks like we should just return None if utxo is not set, now it always raises an exception

python-bitcointx/bitcointx/core/psbt.py

Lines 925 to 929 in 41e25ed

	utxo = self.witness_utxo or self.utxo
	if utxo is None:
	raise ValueError(
	f'utxo is not set for of PSBT_Input at index {self.index}')

a few lines above there's also a check if the index is set on UTXO:

python-bitcointx/bitcointx/core/psbt.py

Lines 921 to 923 in 41e25ed

	if self.index is None:
	raise ValueError(
	'index is not set for PSBT_Input')

index on the input may be unset if someone created PSBT_Input directly and did not supply or did not set the index.

It seems to me that conceptually, in both of this cases we can just return "None" and not throw execption.

The only situation where throwing an exception seems to be of value is when someone needs to make sure that all inputs are signable. But "unsignable" inputs return None in other cases such as unrecognized script, and the check can be accomplished just by iterating over psbt.inputs doing if inp.sign(...) is None:

I think I will just replace raise ValueError(...) with return None in both cases: #53

Let me know if you think that there's a better way to handle this

[AdamISZ]

From my view, I think returning None is right. A caller can always inspect the SignResult object to check (I think?) that the result is as intended. I believe I agree also about index; I don't have such a use case right now, but I could maybe imagine it.

[dgpv]

I released v1.1.1.post2 with the fix