Many thanks for your helpful answer Alan. My only other question is, does there exist a convenient way to unpack a collection of variable length?
If you know that there are 3 elements in the collection, you can specify: play_for(waves(chord[0],chord[1],chord[2]),500) But then if you want to change the number of elements in the list "chord", say from 3 to 5, you have to change the code accordingly. Is there some sort of way to instruct the code to unpack its elements for any number of elements? Like i=len(chord) play_for(waves(chord[0],chord[1],...,chord[i-1]),500) If there is a way to do this it would be great! ----- Original Message ----- From: Alan Gauld <alan.ga...@btinternet.com> Date: Tuesday, January 13, 2009 7:16 pm Subject: Re: [Tutor] A list of input arguments > "Mr Gerard Kelly" <s4027...@student.uq.edu.au> wrote > > >I have a problem with understanding how lists, strings, tuples, > >number > > types and input arguments all interact with each other. > > OK, they are all different types. Some of them take a single value > (sometimes known as a scalar type) and others take a collection > of values (sometimes known as a sequence). Strings are unusual > in that they can be considered as a scalar type or as a collection > of characters! > > Input parameters are simply local variables for the function to > which they are attached. Other than the fact that you can assign > them values from outside the function whe you call it they act just > like normal variables. > > def f(): > print x > > x = 42 > f() > > Is the same (almost)) as > > def f(x): > print x > > > As an example, if I use three arguments, it looks like this: > > > > def main(): > > play_for(waves(440,550,660), 5000) > > > > def main(): > > chord=[440,550,660] > > play_for(waves(chord), 5000) > > > > it doesn't work. > > Because you are passing a single value (a list) into a function that > expects 3 values. > > > It doesn't work with a string or a tuple either. > > Because strings and tuples are also single (container )entities > > You must unpack your collection when calling the function: > > play_for(waves(chord[0],chord[1],chord[2]),5000) > > > The problem is that another part of the code needs to take > > float(chord[0]), that is convert the first input value into the > > float > > class, and the error message says "TypeError: float() argument > must > > be a > > string or a number." > > Thats right, and as you did above you must extract the first element > since the code can't tell that yopu have passed it a collection > instead > of a number! > > > Is there any way to list the input arguments without listing them > > inside > > the function's parentheses? > > No, because the function expects 3 arguments so you must pass it 3. > That is the contract (or interface) that exists betweeen the writer > of > the > function and you the consumer of it. Programming. particularly on > larger projects with multiple teams, is all about defining interfaces > and adhering to them! If you want thebenefit of the function you must > respect its contract. > > HTH, > > > -- > Alan Gauld > Author of the Learn to Program web site > http://www.freenetpages.co.uk/hp/alan.gauld > > > _______________________________________________ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor > _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
