ENH: specify missing keys in KeyError when passing list-like to .loc · Issue #34272 · pandas-dev/pandas (original) (raw)

I'm a big fan of the strong limitation when passing list-likes to .loc[]. However, when the a key is missing and the KeyError is raised, it'd be helpful to know which key/s is/are missing.

I understand this could have performance implications since each key of the list-like object should be searched, but also think the UX would be improved.

At least, the first missing key could be reported, without hindering performance. I'm happy to provide a PR for this if provided with some guidelines (I suppose this affects both Series and DataFrames, as well as maybe some other parts of the code I'm not aware of).

pd.version

'1.0.3'

s = pd.Series({'a': 1, 'b': 2, 'c': 3}) s.loc['d'] # Raises KeyError but specifies 'd' is missing s.loc[['a', 'b', 'c', 'd']] # Raises KeyError without specifying which key is missing