[Tutor] A couple beginner questions.

[Sean 'Shaleh' Perry]

On 25-Sep-2001 Eric Henry wrote:
> Hi there everyone.  I decided work on a small project to sort of get my 
> feet wet in python and programming in general.  I've got a couple of 
> quick questions for you all.  First, is there a built in way to apply 
> some operation to each item in a list?  For example adding 2 to [1,2,3], 
> and getting [3,4,5].
> 

this one is straight from the tutorials.

[1,2,3] is a list in python.  There are two handy functions in python for
lists:

map(func,list) -- every item in list is passed to func() as an argument this is
equivalent to 'for i in list: func(i)'

reduce(func, list) -- starting with the first two elements, pass two elements
to func and keep a cumalitive result.  This is the same as 'total =
func(list[0], list[1]); for i in list[2:]: total = func(total, i)'
 
> Second, I need to store some information from a table.  Each row has 3 
> values.  Somewhat like this:
> 
> [1, 3, 4]
> [2, 4, 5]
> [3, 1, 1]
> 
>  From what I understand, a dictionary would let me assign each of those 
> sets of information a key and retrieve them, but what I need to do is 
> give it say 3 in the second column(the numbers aren't duplicated 
> anywhere in each column) and have it return one or four.  I don't know 
> how clear that all was, but hopefully someone has some idea what I'm 
> talking aobut.
> 

Hmmm, sounds like a homework problem (-:  Consider making the middle element
the key and the each list the data.  So dict[3] -> [1,3,4].  Of course this
only works when the keys are not dups.