Danny Yoo wrote at 15:47 10/10/2005: > > 3) No modularization. Couldn't see a reason to do so. Is there one or > > two? Specifically, what sections should become modules, if any? > > >Hi Dick, > >My recommendation is to practice using and writing functions.
I certainly will, Danny. You've convinced me. And thanks very much for the detailed examples. Dick > For >example, this block here is a good candidate to box off as a named >function: > >####### >F = [] >for word in L: > k = L.count(word) > if (k,word) not in F: > F.append((k,word)) ># F is a list of duples (k, word), where k is the frequency of word >F.sort() >####### > > >That block can be treated as a function that takes in a list of words, and >returns a list of duples. > >###### >def doFrequencyCalculation(L): > # F is a list of duples (k, word), where k is the frequency of word > F = [] > for word in L: > k = L.count(word) > if (k,word) not in F: > F.append((k,word)) > F.sort() > return F >###### > >Here, we explicitly say that frequence calculation depends on having a >list L of words, and that the result should be a list of duples. > >Functions allow us to "scope" variables into different kinds of roles. >We'd say in doFrequenceCalculation that 'word' and 'k' are "temporary" >variables. If we write programs using functions, we can express that >"temporary" role as a real part of the program. > >As it stands, in the original code, we have to watch that 'word' or 'k' >isn't being used by anyone else: like all the other variables in your >program, they're all global and given equal status. You're using >lowercase as an informal way to remind yourself that those variables are >meant to be temporary, but that approach can be error prone. > > >Conceptually, your program appears to work in four stages: > > 1. Read lines of a file > 2. Extract list of words from the lines > 3. Do histogram frequency count on those lines > 4. Report frequency results > >and it would be great if we could see this program flow as an explicit >sequence of function calls: > >################################## >## Pseudocode >def program(): > L = readLinesInFile() > W = extractWordsFromLines(L) > F = doFrequencyCalculation(W) > reportFrequencyResults(F) >################################## > > >This allows one to see the overall program plan without having to read the >whole program. It also allows you to do some experimentation later on by >letting you plugging in different functions in the overall program() plan. > >As a concrete example: once we have a program in this form, it's easy to >swap in a different algorithm for doing frequency calculation: > >###### >def program(): > L = readLinesInFile() > W = extractWordsFromLines(L) > ## F = doFrequencyCalculation(W) > F = doFrequencyCalculationWithDifferentAlgorithm(W) > reportFrequencyResults(F) >###### > > >Does this make sense? Sure does. > Please feel free to ask more questions about this. None right now, thanks. But I can see I need to study the difference between local and global variables. Dick _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
