Skip to main content

Python: dicts vs. classes

I like to "keep it simple stupid" when I'm coding Python. I use classes, but I don't try to shove everything into classes. When all you need is a dict or a list, use a dict or a list. However, I'm coming to think that if you have a bunch of objects that look like the following:

books = [{
  "authors": ["Neil Gaiman"],
  "title": "American Gods",
  "isbn": "9780062113450"
}]

Then it might be time to use a class rather than a dict. In this case, I'd create a class called Book, but I'd put Book instances into a simple list.

Comments

Kevin H said…
I'd use namedtuple for that. But maybe that's just me.
David Goodger said…
For a simple collection of data without specialized behavior, I also use namedtuple, or a "Bunch" class (see the comments for variations). But add in custom behavior (methods), and of course a class is just the ticket. (Of course, namedtuple is just a quick and dirty way to implement a minimal-behavior class. Look up its implementation in the collections module.)

The nice thing about namedtuple (and Bunch) is that when behavior needs to be added, the namedtuple definition can easily be replaced by a class definition, without affecting the rest of the code.
David Goodger said…
The advantage of a Bunch over a namedtuple is that a Bunch is mutable: you can add, remove, and modify attributes in-place. But namedtuple has a built-in order. Your choice.
jjinux said…
Thanks for the comments, guys :)

I thought about using namedtuples, but decided to just go ahead and write out a class. In retrospect, it was the right thing, but my code assumes the instances are mutable.

The Bunch class is nice, but I think have the benefit of creating a class like this is to a) give it a name b) document what attributes you expect to be in it.

It'd be nice if Python had something to let me create a simple class with a set of attributes really quickly, kind of like a case class in Scala.
Craig Maloney said…
I'd love to know how to make a list of classes searchable without having to iterate over each record in turn. Is there a way to do that easily or am I stuck with iterating over lists?
yacc said…
Actually one can just subclass from named tuple, alternatively verbose=True gives you the source to paste.

Named tuples have a number of benefits, a central one being a tuple hence immutable. Add in some properties, and methods and you get a really nice object lite with a slight functional touch (as the value cannot be changed,which makes reasoning about the code so much easier)
Art Zemon said…
If you want something that is "just a little bit" more than a dict, you can create a class derived from a dict. See UserDict http://docs.python.org/2/library/userdict.html
jjinux said…
Thanks for the great comments, yacc and Art!
jjinux said…
> I'd love to know how to make a list of classes searchable without having to iterate over each record in turn. Is there a way to do that easily or am I stuck with iterating over lists?

Do it the same way databases do it. Create indexes of some sort, either via dicts or some sort of tree.

Popular posts from this blog

Ubuntu 20.04 on a 2015 15" MacBook Pro

I decided to give Ubuntu 20.04 a try on my 2015 15" MacBook Pro. I didn't actually install it; I just live booted from a USB thumb drive which was enough to try out everything I wanted. In summary, it's not perfect, and issues with my camera would prevent me from switching, but given the right hardware, I think it's a really viable option. The first thing I wanted to try was what would happen if I plugged in a non-HiDPI screen given that my laptop has a HiDPI screen. Without sub-pixel scaling, whatever scale rate I picked for one screen would apply to the other. However, once I turned on sub-pixel scaling, I was able to pick different scale rates for the internal and external displays. That looked ok. I tried plugging in and unplugging multiple times, and it didn't crash. I doubt it'd work with my Thunderbolt display at work, but it worked fine for my HDMI displays at home. I even plugged it into my TV, and it stuck to the 100% scaling I picked for the othe

ERNOS: Erlang Networked Operating System

I've been reading Dreaming in Code lately, and I really like it. If you're not a dreamer, you may safely skip the rest of this post ;) In Chapter 10, "Engineers and Artists", Alan Kay, John Backus, and Jaron Lanier really got me thinking. I've also been thinking a lot about Minix 3 , Erlang , and the original Lisp machine . The ideas are beginning to synthesize into something cohesive--more than just the sum of their parts. Now, I'm sure that many of these ideas have already been envisioned within Tunes.org , LLVM , Microsoft's Singularity project, or in some other place that I haven't managed to discover or fully read, but I'm going to blog them anyway. Rather than wax philosophical, let me just dump out some ideas: Start with Minix 3. It's a new microkernel, and it's meant for real use, unlike the original Minix. "This new OS is extremely small, with the part that runs in kernel mode under 4000 lines of executable code.&quo

Haskell or Erlang?

I've coded in both Erlang and Haskell. Erlang is practical, efficient, and useful. It's got a wonderful niche in the distributed world, and it has some real success stories such as CouchDB and jabber.org. Haskell is elegant and beautiful. It's been successful in various programming language competitions. I have some experience in both, but I'm thinking it's time to really commit to learning one of them on a professional level. They both have good books out now, and it's probably time I read one of those books cover to cover. My question is which? Back in 2000, Perl had established a real niche for systems administration, CGI, and text processing. The syntax wasn't exactly beautiful (unless you're into that sort of thing), but it was popular and mature. Python hadn't really become popular, nor did it really have a strong niche (at least as far as I could see). I went with Python because of its elegance, but since then, I've coded both p