[Tutor] [OT] Best Practices for Scientific Computing

[Alan Gauld]

On 29/12/14 23:50, Patti Scott wrote:
> Could someone clarify "Modularize code rather than copying and pasting?"

Joel and Danny have given the basic answer in terms of putting
loose code into functions. But it goes a little further too.

You can be tempted to copy/paste functions because they almost
do what you want but not quite (maybe the take a list of values
and you want to use a dictionary). Its easy to copy the function
and change all the numerical indexes into keys and use the
dictionary. But it would be better to change the original function
so that it can work with both, if possible. This usually involves
representing the variations in behaviour as parameters in the
function (usually with defaults to retain the original semantics).

Another case might be where you have a bunch of functions that operate 
on a global data structure. Then you want to have a second similar data 
structure but you can't use the functions on it because they access
the existing global. You could copy/paste the functions and change the 
data reference. But it would be better to either add the data structure 
reference to the functions as a parameter, or you create a class that 
has the data as an internal instance attribute.

Finally, you might have some code in a program that you want to use in 
another program. But you can't just import the first program because
it runs all sorts of other stuff you don't need. So you just copy
out the functions you want. Or you could put the loose code into a 
function (main() usually) and call that within a

if __name__ === "__main__": main()

line in your original program, turning it into a reusable module
which you can now safely import.

So modularize can have several meanings, it applies to any
mechanism used to bundle up code for reuse. The point being that reusing 
code, whether as a function, module or class, is more
flexible and reliable than copy/pasting it.

PS.
Note that reuse is not universally a good thing, it does
have negative aspects too, in test and maintenance costs
and, often, in performance impact. But in the vast majority
of cases the positives vastly outweigh the negatives.

HTH
-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
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