http://www.linuxforums.org/programming/introduction_to_python__part_1.html
Sets
I think I don't really have to explain what a set is, as everyone should know
them from mathematics. It's simply a pile of elements that do not have ordering
and do not contain duplicates.
A set has to be initialized with the elements of a list. Since you already know
what a list is, we do this in one step. Just like with dictionaries, print can
handle a set as it is.
Once we have a set, I show he first useful feature of sets: testing whether an
element is in the set.
inventory_carpenter=set(['helmet', 'gloves', 'hammer'])
print inventory_carpenter # outputs set(['helmet', 'hammer', 'gloves'])
print 'gloves' in inventory_carpenter # outputs 'True'
Since sets are interesting only if we have more that one of them, let's
introduce another one! Once we have that, we can immediately see what are the
elements that both sets contain (intersection).
inventory_highscaler=set(['helmet', 'rope', 'harness', 'carabiner'])
print inventory_carpenter & inventory_highscaler # outputs 'set(['helmet'])'
Similarly, we can have the union of sets ( using | ), difference ( using - ),
or symmetric difference (using ^).
For sets, you don't really need anything else, as you can do every meaningful
operation using the ones above. For example, to add a new element, you can use
union.
inventory_carpenter = inventory_carpenter | set(['nails'])
Using the interpreter interactively
If you would like to try out the things you've learnt right now, you might
appreciate that the interpreter can be used in an interactive way. In case you
use it like that, you don't have to enter your commands to a file, then save
and run it, just tell something to Python, and get the response immediately.
All you have to do is to invoke the interpreter by typing 'python' to
your shell.
[EMAIL PROTECTED]:~$ python
Python 2.5 (r25:51908, Sep 19 2006, 09:52:17)
[GCC 4.1.2 20060715 (prerelease) (Debian 4.1.1-9)] on linux2\n
Type "help", "copyright", "credits" or "license" for more information.
>>>
Once you are here, you can just type anything you like, it will get interpreted
immediately. The good new is that you don't even have to use print if you
want to see the value of a variable, just type the name of it.\n
>>> a\u003d4
>>> a
4
>>>
\n\n",0] ); D(["ce"]); //-->
All you have to do is to invoke the interpreter by typing 'python' to your
shell.
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