new_zoo = ('monkey', 'dolphin', zoo)
print 'Number of animals in the new zoo is', len(new_zoo) print 'All animals in new zoo are', new_zoo
print 'Animals brought from old zoo are', new_zoo[2] print 'Last animal brought from old zoo is', new_zoo[2][2]
$ python using_tuple.py
Number of animals in the zoo is 3
Number of animals in the new zoo is 3
All animals in new zoo are ('monkey', 'dolphin', ('wolf', 'elephant', 'penguin')) Animals brought from old zoo are ('wolf', 'elephant', 'penguin')
Last animal brought from old zoo is penguin
The variable zoo refers to a tuple of items. We see that thelen function can be used to get the length of the tuple. This also indicates that a tuple is a sequence as well.
We are now shifting these animals to a new zoo since the old zoo is being closed. Therefore, the new_zoo tuple contains some animals which are already there along with the animals brought over from the old zoo. Back to reality, note that a tuple within a tuple does not lose its identity.
We can access the items in the tuple by specifying the item's position within a pair of square brackets just like we did for lists. This is called the indexing operator. We access the third item innew_zoo by specifyingnew_zoo[2] and we access the third item in the third item in thenew_zoo tuple by specifyingnew_zoo[2][2]. This is pretty simple once you've understood the idiom.
Tuple with 0 or 1 items. An empty tuple is constructed by an empty pair of parentheses such asmyempty = (). However, a tuple with a single item is not so simple. You have to specify it using a comma following the first (and only) item so that Python can differentiate between a tuple and a pair of parentheses surrounding the object in an expression i.e. you have to specifysingleton = (2 , ) if you mean you want a tuple containing the item2.
A list within a list does not lose its identity i.e. lists are not flattened as in Perl. The same applies to a tuple within a tuple, or a tuple within a list, or a list within a tuple, etc. As far as Python is concerned, they are just objects stored using another object, that's all.