sagemathgh-38160: details in partition.py (code and pep8)
    
just fixing a few pep8 and code details in the modified file

pep8 fixes were mostly scripted using `autopep8`

### 📝 Checklist

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URL: sagemath#38160
Reported by: Frédéric Chapoton
Reviewer(s): Matthias Köppe