[Python] If you add _metadata to a custom subclass of Series, the sequence name is lost when...

pandas 2.2.3

Let’s consider two variants of defining a custom subtype of pandas.Series. In the first one, no custom properties are added, while in the second one, custom metadata is included:

import pandas as pd


class MySeries(pd.Series):

@property
def _constructor(self):
return MySeries


seq = MySeries([*'abc'], name='data')

print(f'''Case without _metadata:
{isinstance(seq[0:1], MySeries) = }
{isinstance(seq[[0, 1]], MySeries) = }
{seq[0:1].name = }
{seq[[0, 1]].name = }
''')

class MySeries(pd.Series):

_metadata = ['property']

@property
def _constructor(self, property=None):
return MySeries


seq = MySeries([*'abc'], name='data')
seq.property = 'MyProperty'

print(f'''Case with defined _metadata:
{isinstance(seq[0:1], MySeries) = }
{isinstance(seq[[0, 1]], MySeries) = }
{seq[0:1].name = }
{seq[[0, 1]].name = }
{getattr(seq[0:1], 'property', 'NA') = }
{getattr(seq[[0, 1]], 'property', 'NA') = }
''')


The output will be:

Case without _metadata:
isinstance(seq[0:1], MySeries) = True
isinstance(seq[[0, 1]], MySeries) = True
seq[0:1].name = 'data'
seq[[0, 1]].name = 'data'

Case with defined _metadata:
isinstance(seq[0:1], MySeries) = True
isinstance(seq[[0, 1]], MySeries) = True
seq[0:1].name = 'data'
seq[[0, 1]].name = None <<< Problematic result of indexing
getattr(seq[0:1], 'property', 'NA') = 'MyProperty'
getattr(seq[[0, 1]], 'property', 'NA') = 'MyProperty'


So, if _metadata is defined, the sequence name is preserved when slicing, but lost when indexing with a list, whereas without _metadata the name is preserved in both cases.

Question: What needs to be done to preserve the name of a custom Series subclass with added metadata when indexing?

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