Foreign For-In, or Python as a First Language

...being a brief recap my experience at the Python Preconference at ALA Annual. In general, the session was a smashing success and I was elated to see a diverse group of people picking up Python so quickly. Without going into details elsewhere, which I think other attendees or organizers will cover, here's one struggle and one pleasant surprise from the preconference.

Explain a For-In Loop

Describing how a for-in loop works was difficult and I repeatedly ran into attendees who just couldn't quite grok it. A Python for-in loop looks like:

for word in wordlist:
    print word

That would loop through the wordlist data structure, which we'll say is a list (similar to an array in other languages), printing each term to the screen. Simple, right? But it's actually pretty weird, because in the above example what exactly is word? It's a local variable that gets a new value each time through the loop. If for-in loops for lists didn't exist in Python, you might implement them like so:

i = 0
while i < len( wordlist ):
    # being super explicit here
    word = wordlist[ i ]
    print word
    i = i + 1

len( wordlist ) here returns the length of the wordlist list, for non-Python people. Otherwise, I assume the syntax is straightforward for anyone who knows a little code. The biggest disadvantage to this implementation is you end up with two variables in the scope—i and word—neither of which is useful after the loop has run.

I'm not sure my explicit for-in loop is more clear to a new programmer, but it's my conceptual model. Students struggled with understanding the for variable's name; where does word come from? In the lecture, Becky Yoose used this example:

for fruit in pies:
    print fruit

The reaction from attendees seemed to be "since pies is a list of different fruits, the variable name has to be 'fruit' here." As if Python was somehow doing natural language processing to figure out a good descriptive term of an individual item in a thematic list. It's a weird thing to grasp conceptually, perhaps the crux being you're getting a variable without any assignment statement. That's a nice convenience for programmers coming from other languages but it obscures what's going on for learners.

Nested Loops & First Languages

On the other hand, I found that a lot of our exercises and final projects involved nested loops, sometimes three to four layers deep. Everyone seemed to absorb this without conceptual difficulty. Maybe it's my own experience speaking here, but I get more and more anxious the deeper my indents go. A lot of this anxiety is based in JavaScript, where blocks wrapped in curly braces tend to take up more space and are harder to parse than in whitespace-happy Python. The uglist code in the world is an instantly-invoked function expression which ends in a bunch of closed code blocks:

            }
        }
    }
}( 'this happens way too often in JavaScript' ) );

Python's conveniences, like range() and how the for-in loop works seamlessly across different data types (lists, dictionaries, even strings. Strings, people!) are a serious boon to beginners. I still think JavaScript makes a great first language for a few reasons: 1) everyone already has it installed via their web browser, so there's zero setup barrier, 2) the web is where data and applications live these days and JavaScript is the language of the web, and 3) a trivial amount of jQuery can make cool things happen. Other languages require more investment before the cool things go down.

But the setup process wasn't an issue for the preconference. We held a help session the night before and only two people came; one of them already had Python installed and on the Windows path, they just needed confirmation that they'd done it right. A number of factors contributed to the ease of setup: many attendees had Macs which typically come with a 2.6.x or 2.7.x version of Python, the Boston Python Workshop docs are great and cross-platform, and a fair portion of attendees were advanced computer users. So with an easy setup, Python (or Ruby) is a sensible choice for a first language.