Python in Education

Obvious Simplicity  |  15

---

store), you’d use constructs called hashtables, associative arrays,

maps or tables. In Python, you use something called a dictionary.

Here’s a data dictionary of a small selection of random capital cities:

capital_cities = {

    'China': 'Beijing'

    'Germany': 'Berlin',

    'Greece': 'Athens',

    'Russia': 'Moscow',

    'United Kingdom': 'London',

}  

I’ve simply assigned the dictionary to the 

capital_cities

 object. If

I want to look up a capital city for a certain country, I reference the

country’s name in square brackets next to the object named 

capi

tal_cities

:

capital_cities['China']

'Beijing'

Many programming languages have data structures that work like

Python’s lists and dictionaries; some of them do the obvious thing

and call such constructs “lists” and “dictionaries”; some other lan‐

guages make using such constructs as easy and obvious as Python

(although many don’t). Python’s advantage is that 

it does all three of

these things

: it has useful data structures as a core part of the lan‐

guage, it gives them obvious names, and makes them extraordinarily

easy to use. Such usefulness, simplicity and clarity is another case of

removing barriers to engaging with programming.

As mentioned earlier, Python also does the expected thing. For

example, if I try to sum together an empty dictionary and an empty

list (something that’s obviously wrong—evidence that I’ve misun‐

derstood what I’m trying to do) Python will complain:

>>> {} + []

Traceback (most recent call last):

  File "", line 1, in

TypeError: unsupported operand type(s) for +: 'dict' and 'list' 

This is simply telling me that I can’t use the “+” operand to sum a

dictionary and a list. This is to be expected, rather obvious and quite

helpful.

Nevertheless, other languages try to be less strict and more forgiving

of the programmer. While this may sound like a good idea, it means

that faulty code like that attempted above will be executed without

any error and cause uncertain results (after all, what is the answer of