Data Structures in Python

by Alex Gaynor

Python is awesome because it implements basic data structures as described by Knuth.

Paraphrase: The Python core has read Knuth so we don’t have to!

Alex Commandments

  1. Use types idiomatically
  2. Sometimes you don’t get a choice
  3. Be efficient, when it doesn’t cost you anything
  4. sometimes you habe more than one concern to deal with. The standard lib can help!
  5. Don’t do more than you have to: are there to help.


  • list vs tuple
  • list vs set
  • set vs frozenset

list vs tuple

“I only use tuples if using a namedtuple would be equally appropriate”

Not a performance or mutability issue, but use them idiomatically

sets vs lists

  • lists have an order, sets don’t
  • sets must be hashable
  • sets let you check for uniqueness super-fast

sets vs frozenset

blah blah

The stdlib


  • new in 2.7

  • For when you have a dict that needs an order

  • Syntax:

        ("state": Field),


  • Fact: list.pop(0) and list.insert(0) are slow
  • Good for in memory logs and such


  • Array: Good for a bunch of types of the same sort
  • heapq: Look into it.

Do It Yourself

When you have to do it yourself use!

  • abstract base classes for extending collections

  • Because you don’t subclass dict ever!!!!

    • Subclassing Python’s builtin containers tends not to behave as we want
    • Subclassing the ABCs does
  • OrderedSet example: