Welcome to Computer Programming For Kids (CP4K)

Welcome to the Computer Programming for Kids blog! We are the co-authors of the book "Hello World! Computer Programming for Kids and Other Beginners", released in March 2009. The book is published by Manning Publications. Manning has a web site for the book, which is where you can download the software and other files related to the book. You can purchase it here, at the Manning web site. If you use this link to purchase the print book or e-book from the Manning web site, you can use the discount code aupromo40 at checkout to get a 40% discount. You can also get it through online retailers like Amazon, as well as in many retail locations such as Chapters in Canada and Barnes & Noble in the U.S. This blog is mostly about the book (for now), but anything related to computers and programming, particularly for kids and beginners, is fair game. We will post articles with extra material that didn't make it into the book, and reader feedback and suggestions are always welcome.

Thursday, March 11, 2010

Passing arguments as a list

In the Author Forum on the Manning page for the book, someone asked about passing arguments to a function as a list. Since posting code on that forum doesn't work well, I thought I would post the answer here.

If you are passing a number of arguments to a function, you could pass them as individual arguments, like this:

def printMyLuckyNumbers(num1, num2, num3, num4, num5):
print "Here are your lucky numbers:"
print num1, num2, num3, num4, num5

Then you would call the function like this:

printMyLuckyNumbers(3, 7, 10, 14, 27)

But that has a couple of disadvantages. First, if there are a lot of arguments, it gets messy to type all the variable names. Second, you might not know ahead of time how many arguments you want to pass.

So, another way, that solves both those problems, is to pass a list of arguments instead, like this:

def printMyLuckyNumbers(myNums):
print "Your lucky numbers are:"
for num in myNums:
print num,

Then you would call the function like this:

myLuckyNumbers = [3, 7, 10, 14, 27]

In the first example, you are passing 5 separate arguments. In the second example, you are passing a single list. That list happens to have 5 items, in this example. But it would work with any number of items. For example, this would work just fine when calling the second version of the function:

myLuckyNums = [2, 3, 5, 7, 10, 27, 32, 45]

These are very simple examples. You can pass things more complicated than lists. You can pass nested lists (lists of lists, or two-dimensional lists). You can pass objects, which can contain any data structure you care to define. You can pass lists of objects or objects containing lists (or dictionaries, or any other Python data type).