[python-package] take shallow copy of dataframe in predict (fixes #6195) #6218
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Takes a shallow copy of the dataframe in the
_data_from_pandas
function to avoid modifying it when converting categorical features to their codes. This used to always be done (implicitly) for predict until #6066, since the function is called withfeature_name='auto'
and thecopy
argument ofpandas.DataFrame.rename
is passed as thedeep
argument topandas.DataFrame.copy
, however that behavior wasn't obvious.Fixes #6195.
Also updates the test that verifies the original dataframe isn't modified to now consider the case of unseen categories, which fails in the current master and should prevent #6195 from happening again.