Uses for Dynamic Languages

Question

My primary language right now is D, and I'm in the process of learning Python because it's required for a course I'm taking. While I understand why dynamic languages would be a breath of fresh air for people programming in static languages without type inference or templates (IMHO templates are to a large extent compile-time duck typing), I'm curious what the benefits are of dynamic languages even when you have those.

The bottom line is that, if I'm going to learn Python, I want to learn it in a way that really changes my thinking about programming, rather than just writing D in Python. I have not used dynamic languages since I was a fairly novice programmer and unable to appreciate the flexibility they supposedly offer, and want to learn to take full advantage of them now. What can be done easily/elegantly in a dynamically typed, interpreted language that's awkward or impossible in a static language, even with templates, polymorphism, static type inference, and maybe runtime reflection?

Answer 1

I find dynamic languages like Perl and to a lesser extent Python allow me to write quick and dirty scripts for things I need to do. The run cycle is much shorter in dynamic languages and often less code needs to be written then in a statically typed language which increases my productivity. This unfortunately comes at the cost of maintainability but that is a fault of the way I write programs in dynamic languages not in the languages them selves.

Answer 2

With a dynamic language it's much easier to have a command line interpreter so you can test things on the command line and don't have to worry about a compile step to see if they work.

Answer 3

"I'm curious what the benefits are of dynamic languages even when you have those."

Compared to D programming language:

• Python is a more compact language. It allows you to express as much as D but it uses many fewer different concepts to achieve it -- less is more.

• Python has a powerful standard library -- batteries included.

I don't know whether D has interactive prompts but in Python an interactive shell such as ipython is an integrated part of development process.

Answer 4

Take a look at this e4x example in JavaScript:

var sales = <sales vendor="John">
    <item type="peas" price="4" quantity="6"/>
    <item type="carrot" price="3" quantity="10"/>
    <item type="chips" price="5" quantity="3"/>
  </sales>;

alert( sales.item.(@type == "carrot").@quantity );
alert( sales.@vendor );
for each( var price in sales..@price ) {
  alert( price );
}

Especially, take a look at line:

alert( sales.item.(@type == "carrot").@quantity );

In typical static languages, you don’t get to write sales.item, since you can not know that item is property of sales until runtime. This is not limited to e4x. You get to program in similar style when connecting when writing SOAP clients or any other underlying type you do not know until runtime. In a static language, you would typically need to run a tool that will generate stub classes or program in a very verbose way. Then, if something changes in a web service, you need to regenerate stubs all over again. Take a look at java DOM code:

import org.dom4j.Document;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;

public class Foo {

    public Document createDocument() {
        Document document = DocumentHelper.createDocument();
        Element root = document.addElement( "root" );

        Element author1 = root.addElement( "author" )
            .addAttribute( "name", "James" )
            .addAttribute( "location", "UK" )
            .addText( "James Strachan" );

        Element author2 = root.addElement( "author" )
            .addAttribute( "name", "Bob" )
            .addAttribute( "location", "US" )
            .addText( "Bob McWhirter" );

        return document;
    }
}

Definitely much more verbose than your dynamic code. And, of course, it is not statically typed. There is no way to check that you misspelled “author” as "autor" until runtime. All this verbosity is essentially there to let you capture something that is dynamic in nature in static style.

I think this is one of the strong points of dynamic languages.

Answer 5

I actually wrote a blog post on this: linky. But that post basically can be summed up like this:

You'd be surprised at how much of a load off your mind it is to not have to name at compile time what type your variable is. Thus, python tends to be a very productive language.

On the other hand, even with good unit tests, you'd also be surprised at what kinds of stupid mistakes you're allowing yourself to make.

Answer 6

Example in Python:

def lengths(sequence):
    try:
        return sum(len(item) for item in sequence)
    except TypeError:
        return "Wolf among the sheep!"

>>> lengths(["a", "b", "c", (1, 2, 3)])
6
>>> lengths( ("1", "2", 3) )
'Wolf among the sheep!'

How long do you think this took me to write, and how many compile-run-debug cycles?

If you think my example is trivial, I can reply by saying that dynamic languages make trivial many programming tasks.