Redundant type checks and dead code requiring refactoring #63119
Description
While reviewing /pandas/tests/io/parser/test_na_values.py, I found a redundant nested type check in test_na_values_scalar(all_parsers, na_values, row_data) with an unreachable branch:
if parser.engine == "pyarrow" and isinstance(na_values, dict):
if isinstance(na_values, dict): # redundant because isinstance(na_values, dict) must be True
err = ValueError
msg = "The pyarrow engine doesn't support passing a dict for na_values"
else: # unreachable
err = TypeError
msg = "The 'pyarrow' engine requires all na_values to be strings"
with pytest.raises(err, match=msg):
parser.read_csv(StringIO(data), names=names, na_values=na_values)
return
elif parser.engine == "pyarrow":
msg = "The 'pyarrow' engine requires all na_values to be strings"
with pytest.raises(TypeError, match=msg):
parser.read_csv(StringIO(data), names=names, na_values=na_values)
return
It seems that the inner implementation was not updated when refactoring the outer code. I am not sure whether the intended code should be:
if parser.engine == "pyarrow" and isinstance(na_values, dict):
msg = "The pyarrow engine doesn't support passing a dict for na_values"
with pytest.raises(ValueError, match=msg):
parser.read_csv(StringIO(data), names=names, na_values=na_values)
return
elif parser.engine == "pyarrow":
msg = "The 'pyarrow' engine requires all na_values to be strings"
with pytest.raises(TypeError, match=msg):
parser.read_csv(StringIO(data), names=names, na_values=na_values)
return