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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Thu, 25 Jun 2015 14:56:54 -0600
Subject: Re: Reference Counting Irregularity
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Xref: csiph.com comp.lang.python:93165

On Thu, Jun 25, 2015 at 12:49 PM, Eric Edmond <t-erice@microsoft.com> wrote=
:
> Hi,
>
> I have been writing a C++ extension for Python recently, and am currently
> fixing the reference counting throughout the extension. As I am very new =
to
> this topic, my question may have a simple answer, but I was unable to fin=
d
> any mention of the behavior online.
>
> When using the PyObject_GetItem(obj, key) function, I noticed inconsisten=
t
> behavior with various types of obj (for reference, key is always a str
> object). When obj is a standard dictionary, the key=E2=80=99s reference c=
ount
> remains unchanged, as expected. However, when obj is a pandas DataFrame
> object, the key=E2=80=99s reference count increases by 2. This could very=
 well be by
> design of the DataFrame object doing some internal caching of the string,
> but does not appear in the documentation, so I thought I would bring up t=
he
> issue.

What is your question? If you want to know why 2 is added to the
reference count for pandas objects, the first place to check would be
with the pandas developers, as PyObject_GetItem is just going to call
the implementation for that type. You can find the CPython code here:

https://hg.python.org/cpython/file/9aad116baee8/Objects/abstract.c#l136