Kids, Code, and Computer Science Magazine

How to Keep Your Code DRY

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DRY is an acronym for Don't Repeat Yourself. It's a critical programming concept and skill to learn.

Here’s how it works in real life. Plus a DRY joke at the end.

Imagine you’re a programmer. Someone has asked you to write code to generate a random number between 1 and 1000. The random number is to be used by another bit of code. You sit down and write simple clean code to generate a random number:

nbr = create_rnd_nbr(1,1000)
print nbr

where create_rnd_nbr is a built in function included in the programming language which expects a start number (1) and end number (1000) to be passed into it. You assign the result of create_rnd_nbr(1,1000) to the variable named nbr then print the variable as a number to your computer screen.

A month passes, you’re busy, and they ask you to write another bit of code to generate a random number between 1 and 500 to be used by another part of the application. You could adapt the code you have to work in both cases, for numbers between 1 and 1000 and 1 and 500. But you’re busy. So you copy paste your oode and change the limit from 1000 to 500:

nbr = create_rnd_nbr(1,1000)
print nbr

new_nbr = create_rnd_nbr(1,500)
print new_nbr

Now you have two blocks of code that generate random numbers.

Imagine this happens a third and fourth time. You have four different blocks of code to generate random numbers. Time passes, you leave the company, and a few years later the company hires a new programmer. Someone has noticed the application generates weird random numbers. They think its the random number code you wrote.


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