>  To: tutor@[...].org
>  From: alan.gauld@[...].com
>  Date: Wed, 22 Jul 2009 08:46:04 +0100
>  Subject: Re: [Tutor] code structure terminology and advice
>  
>  
>  "Che M" <pine508@[...].com> wrote 
>  
>  You pretty much answered your own question.
>  
>  The ultimate answer depends on a few other contextual issues.
>  
>  > Q1) Generally, what is the best structure for when there are 
>  > a number of steps/actions that need to be taken?  
>  
>  A sequence! :-)
>  
>  > Q2) Is there a term/some jargon in programming that 
>  > refers to the difference between examples 1-3 below?
>  
>  Not that I'm aware of.
>  
>  >  wish to perform four related sequential actions--steps, 
>  > let's call them--in some part of the program.  
>  
>  If the entire program consists of those 4 steps (as in a batch 
>  data processing program, say) then you might structure things 
>  differently than if the 4 steps are only part of a bigger 
>  program - one menu option out of several, say.
>  
>  In the former you would perform the steps in sequence and 
>  may or may not put them in functions.depending on whether 
>  they would ever be reused and how long the code was per step.
>  In most cases the steps are likely to be reusable or of significant 
>  length so you would put each one in its own function.
>  
>  > 1. Do the steps all in one function:
>  > 
>  > def Function(self):
>  >   do step1 action
>  >   do step2 action
>  >   do step3 action 
>  >   do step4 action
>  
>  This would be sensible in the menu selection context.
>  
>  > 2. Have each step be a function, and have each function 
>  > call the next function in the chain:
>  
>  No, this is terrrible from every point of view. It removes any 
>  opportunity of reuise of individual steps and builds up a deep 
>  call stack which makes debugging harder and the coupling 
>  between functions makes maintenance harder (for example 
>  swapping two steps around in the sequence)
>  
>  > def StepOne(self):
>  >    do step1 action
>  >    StepTwo()
>  
>  > 3. Make each step a function, but call all of them in order in 
>  > one master function:
>  > 
>  > def MasterFunction(self):
>  >    self.StepOne()
>  >    self.StepTwo()
>  
>  This is just a variation on option 1 and the same applies.
>  
>  The fourth option you do not consider but which could be the 
>  best solution for the batch program I discussed is just to perform 
>  each step from the top klevel of the program, ie no 
>  enclosing function
>  
>  StepOne()
>  StepTwo()
>  StepThree()
>  StepFour()
>  
>  
>  > It seems to me that example 3 is the most sensible.  
>  
>  In general yes.
>  
>  > 1 is bad because the steps should be functions, because then they 
>  > can be easily reused, seen from an IDE explorer, etc. 
>  > (I guess if they are really minor things it isn't necessary). 
>  
>  This depends on the size of the steps and the nature of the overall 
>  programme, but functions would usually be best.
>  
>  > 2 is terrible 
>  
>  Yes.
>  
>  > Maybe there are other and better ways to think about organizing 
>  > a sequence of steps, and if so I'd love to hear them.  
>  
>  For longer and more complex processes you could use a table 
>  or list of functions and step through them in a loop
>  
>  process = [StepOne, StepTwo,...., stepN]
>  
>  for step in process:
>       step()
>  
>  Or for dynamically changing sequences you can create or hold 
>  a sequence list and use that to index a list of steps:
>  
>  steps = [StepOne, StepTwo,...., stepN]
>  sequence = [1,2,3,4]
>  
>  def do Process(sequence)
>      for step in sequence:
>           steps[step]()
>  
>  This allows you to selectively peform some of the steps:
>  
>  sequence = [1,3,4,N]
>  
>  doProcess(sequence)
>  
>  Finally for very complex scenarios you might implement a 
>  state machine where the return value of each step controls 
>  the next step in the sequence. That can be done by building 
>  a set of state objects or using a data driven approach with 
>  a table
>  
>  You can read about state machines in several places, 
>  I'd start with Wikipedia.
>  
>  You might also find that reading about business process execution
>  languages gives you some ideas about how to structure and 
>  represent complex processes. BEPL would be a good 
>  starting point, again try Wikipedia.
>  
>  HTH,
>  
>  
>  -- 
>  Alan Gauld
>  Author of the Learn to Program web site
>  http://www.alan-g.me.uk/

Thank you, Alan.  It is sometimes helpful just to get corroboration, and I feel that sometim
es the simplest things are the most important.  I also thought that maybe the mistake in exa
mple 2 had a name; I don't know if it is a common mistake or not for beginning programmers, 
but I have found myself doing it sometimes and I am making a point to undo it now in any old
 code.  The point about looping through a list of functions is also something that hadn't oc
curred to me.  So this is all very helpful.

Thanks,
Che

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