[Python] _metadata properties do not work with pyjanitor

_matadata original properties are not pased to pyjanitor manipulation results

Take the following MWE:

import pandas as pd
import janitor # noqa: F401
import pandas_flavor as pf

# See: https://pandas.pydata.org/pandas-docs/stable/development/extending.html#define-original-properties
class MyDataFrame(pd.DataFrame):

# normal properties
_metadata = ["myvar"]

@property
def _constructor(self):
return MyDataFrame

@pf.register_dataframe_method
def regvar(self):
obj = MyDataFrame(self)
obj.myvar = 2
return obj

@pf.register_dataframe_method
def printvar(self):
print(self.myvar)
return self

df = pd.DataFrame(
{
"Year": [1999, 2000, 2004, 1999, 2004],
"Taxon": [
"Saccharina",
"Saccharina",
"Saccharina",
"Agarum",
"Agarum",
],
"Abundance": [4, 5, 2, 1, 8],
}
)


Now:

df2 = df.regvar().query("Taxon=='Saccharina'").printvar()


This correctly returns 2.

However:

index = pd.Index(range(1999,2005),name='Year')
df2 = df.regvar().complete(index, "Taxon", sort=True).printvar()


Returns an Exception:

---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
~\AppData\Local\Temp\ipykernel_4412\627945022.py in ?()
39
40 df2 = df.regvar().query("Taxon=='Saccharina'").printvar()
41
42 index = pd.Index(range(1999,2005),name='Year')
---> 43 df2 = df.regvar().complete(index, "Taxon", sort=True).printvar()

HOME\venvs\base\Lib\site-packages\pandas_flavor\register.py in ?(self, *args, **kwargs)
160 object: The result of calling of the method.
161 """
162 global method_call_ctx_factory
163 if method_call_ctx_factory is None:
--> 164 return method(self._obj, *args, **kwargs)
165
166 return handle_pandas_extension_call(
167 method, method_signature, self._obj, args, kwargs

~\AppData\Local\Temp\ipykernel_4412\627945022.py in ?(self)
21 @pf.register_dataframe_method
22 def printvar(self):
---> 23 print(self.myvar)
24 return self

HOME\venvs\base\Lib\site-packages\pandas\core\generic.py in ?(self, name)
6295 and name not in self._accessors
6296 and self._info_axis._can_hold_identifiers_and_holds_name(name)
6297 ):
6298 return self[name]
-> 6299 return object.__getattribute__(self, name)

AttributeError: 'DataFrame' object has no attribute 'myvar'

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