Fix import

[giacomocaironi]

• Fix import of script module
• Make Tx fail assert_valid() when there are no inputs or outputs

[sourcery-ai]

Sourcery Code Quality Report

❌  Merging this PR will decrease code quality in the affected files by 0.30%.

Quality metrics	Before	After	Change
Complexity	3.64 ⭐	3.65 ⭐	0.01 👎
Method Length	92.97 🙂	93.94 🙂	0.97 👎
Working memory	8.26 🙂	8.38 🙂	0.12 👎
Quality	64.82% 🙂	64.52% 🙂	-0.30% 👎

Other metrics	Before	After	Change
Lines	1680	1697	17

Changed files	Quality Before	Quality After	Quality Change
btclib/alias.py	75.39% ⭐	73.96% 🙂	-1.43% 👎
btclib/b32.py	72.21% 🙂	72.21% 🙂	0.00%
btclib/hashes.py	85.49% ⭐	85.98% ⭐	0.49% 👍
btclib/psbt/psbt.py	61.12% 🙂	61.12% 🙂	0.00%
btclib/script/__init__.py	53.98% 🙂	53.98% 🙂	0.00%
btclib/script/taproot.py	65.01% 🙂	64.83% 🙂	-0.18% 👎
btclib/tx/tx.py	74.62% 🙂	74.33% 🙂	-0.29% 👎
tests/tx/test_tx.py	59.35% 🙂	58.55% 🙂	-0.80% 👎

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
btclib/psbt/psbt.py	Psbt.assert_signable	22 😞	163 😞	11 😞	40.42% 😞	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
btclib/psbt/psbt.py	Psbt.parse	10 🙂	188 😞	15 😞	41.77% 😞	Try splitting into smaller methods. Extract out complex expressions
tests/tx/test_tx.py	test_tx	0 ⭐	754 ⛔	13 😞	44.57% 😞	Try splitting into smaller methods. Extract out complex expressions
btclib/script/taproot.py	check_output_pubkey	8 ⭐	212 ⛔	11 😞	47.79% 😞	Try splitting into smaller methods. Extract out complex expressions
btclib/psbt/psbt.py	join_psbts	5 ⭐	158 😞	16 ⛔	48.14% 😞	Try splitting into smaller methods. Extract out complex expressions

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