What Features of Python Do I Use?

It’s easy to answer the question in this post’s title for the Python version Software Design by Example using Python’s ast module:

import ast
import sys
from collections import Counter

def main():
    seen = Counter()
    for filename in sys.argv[1:]:
        scrape(filename, seen)
    for count, name in sorted(seen.items(), key=lambda x: x[1], reverse=True):
        print(name, count)

def scrape(filename, seen):
    with open(filename, "r") as reader:
        tree = ast.parse(reader.read(), filename=filename)
        for node in ast.walk(tree):
            seen[node.__class__.__name__] += 1

if __name__ == "__main__":
    main()

The results shown below reveal that the book uses a rather small subset of Python’s features. These tables is misleading, though, since things like decorators and else don’t show up. Still, I think these numbers show that:

1. I’m pretty conservative in my Python coding.
2. It’s possible to teach a lot about design without using a lot of language features.
3. Which implies that it’s possible do a lot of design with a fairly small language.

As I wrote a couple of days ago, I’m not going to write another programming book. If I had it all to do over again, though, I’d think very seriously about doing just one volume in Lua: Roberto Ierusalimschy and his team have done us all a service in resisting the bloat that almost every other language has succumbed to.

And here are the uninteresting bits (e.g., intermediate nodes in the parse tree or specific arithmetic operators):

Update: in memory of Niklaus Wirth, Dana Sibera has reproduced the classic Apple Pascal poster (see below). Like I said, I’m not going to write another programming book, but if I did, I’d want to use a language whose grammer is no more complicated than this.