Pointers? In My Python? It's More Likely Than You Think

Eli Holderness (~eli)


Elevator pitch:

Ever wondered about the difference between is and ==, or why you might need to use deepcopy? Maybe you’ve been stumped by a variable changing when you didn’t expect it to, or an interview question about object lifetimes. Or, perhaps, you just really want to see some tuples behaving badly.

Join me for a tour of some of CPython’s dark memory magic and unintuitive behaviours, where we’ll find out:

What pointers are and where you’ll see them in your code; What the id of a Python object is, and why it matters; How CPython can tell when you’re done using an object, and what happens next

No C knowledge required.

Longer abstract

Python is a wonderful thing that takes all the complication of memory management away from us. We don’t have to worry about pre-allocating memory for our objects, or remember to free it once we’re done. So, given that we’re not doing it manually, how do these things happen? Do we have to care? Well, sometimes. Maybe.

In this talk, we’ll discuss what a pointer is, where they crop up in Python, and what you need to know in order to avoid getting tripped up by them. We’ll also cover the id of an object, how it varies between different implementations like IronPython and PyPy, and why is is different from ==. Finally, we’ll talk about garbage collection, what reference counting is, and how CPython knows when it’s time to get rid of unused objects.

Whether you just want to understand what’s going on under the hood without having to dive into the implementation, or you’re on the hunt for some new diabolical things to do with code (self-referential lists are only the beginning!), come along to this talk and learn about the pointers in your Python.

This talk is aimed at anyone with an interest in how Python handles objects in memory, or who’s ever been confused by side-effects popping up in their code. Absolutely no knowledge of C is required, and Python beginners are extremely welcome.

Outline and timings

  • Introduction - 2 Minutes
  • What is a pointer? - 2 minutes
  • Odd behaviour with pointers - 5 minutes
  • Object IDs - 8 minutes
  • Reference counting - 3 minutes
  • Garbage collection - 5 minutes
  • Time for questions - 5 minutes


No prerequisites; Python beginners welcome. No domain-specific knowledge required.

Video URL:


Speaker Info:

I've spoken at Python Web Conference 2021 about WFH with ADHD, and am lined up to speak about building web apps using only Python at PyCon Namibia this June.

Speaker Links:


Section: Core Python
Type: Talks
Target Audience: Beginner
Last Updated: