Why are attributes lost after copying a Pandas DataFrame

Question

Why is it not possible to pass attributes of an instance through a copy? I want to pass the name attribute to another dataframe.

import copy
df = pd         


        

Answer 1

The copy.deepcopy will use a custom __deepcopy__ method if it is found in the MRO, which may return whatever it likes (including completely bogus results). Indeed dataframes implement a __deepcopy__ method:

def __deepcopy__(self, memo=None):
    if memo is None:
        memo = {}
    return self.copy(deep=True)

It delegates to self.copy, where you will find this note in the docstring:

Notes
-----
When ``deep=True``, data is copied but actual Python objects
will not be copied recursively, only the reference to the object.
This is in contrast to `copy.deepcopy` in the Standard Library,
which recursively copies object data (see examples below).

And you will find in the v0.13 release notes (merged in PR 4039):

__deepcopy__ now returns a shallow copy (currently: a view) of the data - allowing metadata changes.

Related issue: 17406.