[Tutor] How to print certain elements

[Mkhanyisi Madlavana]

How would I print washington and monroe using   [:]?
print X[::3]
How would I print every element but those two names?
print X[1::2]


On 21 January 2014 12:18, Alan Gauld <alan.gauld at btinternet.com> wrote:

> On 21/01/14 06:18, Adriansanchez wrote:
>
>> Hello everyone,
>> I am newbie to Python and programming in general. My question is, given a
>> list:
>> X=['washington','adams','jefferson','madison','monroe']
>> And a string:
>> Y='washington,adams,jefferson,madison,monroe'
>>
>> How would I print washington and monroe using   [:]?
>> How would I print every element but those two names?
>>
>
> The [:] syntax is used for selecting a range of values
> from a starting point to a finish.  Its not appropriate
> for selecting arbitrary items out of the list.
>
> If you know which items you want you can use a simple
> index to access them (remember the first item is index 0)
>
> So to print the first item and the fourth item:
>
> print(X[0],X[3])
>
> In your case it's the first and last so we can do
> a similar thing:
>
> print(X[0], X[4])
>
> But for the last element we can alternatively use
> a shortcut to save counting the indexes; that's use
> an index of -1:
>
> print(X[0],X[-1])
>
> Printing every element except those two is harder.
> The simplest approach is to use a loop to process
> the list and test each value:
>
> for name in X:
>     if name not in (X[0], X[-1]):
>        print name
>
> For the special case of excluding the first and
> last names you could use the [:] notation like
> this:
>
> print X[1:-1]
>
> But that only works where you want *all* the
> names in a sequence between two end points.
>
> Finally there is a more advanced way of filtering
> out items from a list called a list comprehension:
>
> print ( [name for name in X if name not in (X[0],X[-1])] )
>
> Which is pretty much our 'for' loop above, written in
> a shorthand single line form.
>
> hth
>
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.flickr.com/photos/alangauldphotos
>
>
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