Help With map() *He says while pulling his hair out*

[Alex Martelli]

"EricIDLE" <grayson-wilson at home.com> wrote in message
news:pM927.657463$166.13605776 at news1.rdc1.bc.home.com...
> Ok first off I have a wee problem with one of the examples in my book it
is
> as follows:
>
> s="12.19.6.7.12"
> ls = string.split(s, '.')
> md = map(string.atoi, ls)
>
> Ok. well the problem is basically the whole thing. I know s="12.19.6.7.12"
> is just defining the varible 's' with the numbers. But my first problem is

Specifically, variable s is being bound to a string made up of several
DIGITS and periods.  "Number" is an ambiguous terms, while "digit"
more precisely identifies one of the characters '0', '1', ... '9' (note
the quotes).

> after string.split in its argument I know what the S means but I dont know
> what the '.' means does that mean to remove all the periods?

No, it means to SPLIT where a period occurs.  The result of string.split
is then a list of strings, each a copy of the substring of s that occurs
between two periods.

> The second problem is that I dont quite grasp the map() function what
> exactly does it do, In its argument it says in lamens terms "Turn the
string
> ls into intergers" my problems is wasent it always intergers? I mean the

ls is a list of strings.  string.split always returns a list of strings --
specifically, copies of substrings of s.

> varible ls contains ['12', '19', '6', '7', '12'] arent those intergers
they

No, they are strings (which happen to be made up of digits, only, in
this case).  The quotes around each are a strong indication of their
string nature.

If you need to transform a string of digits into an integer number,
you can pass the string of digits to function int (or, as here used,
function string.atoi).  map() calls its first argument (normally a
function) over each item in its second argument (a sequence) and
returns the list of results  (map also has other uses, but this is
one fundamental use for it).


Alex