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"""tuples http://openbookproject.net/thinkcs/python/english2e/ch11.html#tuples-and-mutability """

1. A tuple is like a list - it is a sequence of elements that can be accessed
2. by their index.
3. The difference - tuples are immutable
4. A tuple can be defined using syntax similar to a list, with
5. parentheses replacing square brackets:

tup = (1, 5, 10, 20)

1. it is possible to eliminate the parentheses:

tup = 1, 5, 10, 20

1. It is slightly tricky to create a tuple with a single element:

tup = 5,

1. or

tup = (5,)

1. tuples support the same indexing and slice operations as strings and lists
2. like lists you can't modify a tuple:

tup = ('a', 'b', 'c', 'd', 'e')

1. now try modifying tup[0]:

tup[0] = 'z'

1. when returning multiple objects from a function, you typically do so
2. as a tuple:

def myfunc() :

    return 3,5,10

1. you can now call this function as:

x,y,z = myfunc()

1. or

tup = myfunc()

1. and check that this is indeed a tuple:

print type(tup)

1. tuples are particularly useful as keys for dictionaries

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