----------------------------- On Tue, Dec 30, 2014 12:34 PM CET Alan Gauld wrote:
>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). But isn't there a point where you break the 'law' that a function should have one and only one goal? At a certain point you end up with a big fat juicy function that not only takes dicts and lists, but also scratches your back, does the laundry,... >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 Say you have a file 'helpers.py' that contains functions that you might use across projects. How do you only display the functions that you actually used in your (Sphinx) documentation of a particular project? >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. I often use python for data analysis. I would be afraid that a modification to a generic function for project B would affect the results of project A (which may be long-running analysis). Hmmm, maybe 'git submodule' would be useful here. 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 >Follow my photo-blog on Flickr at: >http://www.flickr.com/photos/alangauldphotos > > >_______________________________________________ >Tutor maillist - Tutor@python.org >To unsubscribe or change subscription options: >https://mail.python.org/mailman/listinfo/tutor _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
