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.ga...@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 > > > _______________________________________________ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > https://mail.python.org/mailman/listinfo/tutor >
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