* Lists
*** Outline
***** Lists
***** Tuples
***** Arsenal Required
*** Script
    Welcome friends. 
    
    In previous tutorial we covered Lists and Tuples and related 
    functions. In this session we will continue with Python supported
    data structures and cover Dictionaries and sets. We have already 
    covered some basics of Dictionaries in session on Statistics. Here
    we will revisit those concepts and some new ones. 
    
    We give it a name and it should return a corresponding number. 
    Dictionaries are just key-value pair. For each 'key' there is
    corresponding 'value'. In lists we have indexes to access elements,
    here we have 'key'. 
    
    '{}' are used to create Python dictionaries. Lets start by opening 
    IPython interpreter. Lets create a dictionary say

    player = {'Mat': 134,'Inn': 233,
    'Runs': 10823, 'Avg': 52.53}
    Its dictionary storing statistics of a cricket player.
    Now to get the 'average' of this player we have to simply write
    print player['Avg']
    52.53

    To add a new key-value to this dictionary we have to something like
    player['Name'] = 'Rahul Dravid'
    print player    
    Please dont forget that Python dictionaries dont maintain the order
    in which key-value pair are stored it changes as we add new entries.

    In dictionaries Duplicate keys are overwritten, that is when we do 
    player['Mat'] = 139
    It wont create a new entry, rather it will simply overwrite previous
    value with new one. So
    print player
    will have updated value

    As we covered in one of previous sessions to iterate through lists 
    we use 'for'. In case of dictionaries we can iterate over them using 
    'keys' for example
    for key in player:
        print key, player[key]
    We saw how containership works in lists, there we can check if a 
    value is present in list or not, in case of Dictionaries it works
    only for keys. so
    'Inn' in player
    returns True
    'Econ' in Player
    returns False as there is no such 'key'
    If you try to look or search 'value' it wont work.
    Dictionaries supports some functions to retrieve keys and values 
    like
    player.keys()
    returns the list of all 'keys'
    player.values()
    return list of all 'values'    

    Next we shall look at 'sets'. Sets in Python are unordered 
    collection of unique elements. This data structure comes handy in
    situations while removing duplicates from a sequence, and computing 
    standard math operations on sets such as intersection, union, 
    difference, and symmetric difference. 
    
    Lets start by creating a set
    f10 = set([1,2,3,5,8])
    f10 is set of Fibonacci numbers less then 10
    lets print value of f10
    print f10

    As we mentioned earlier, these are unordered structure so order of
    elements are not maintained, and output order is different than 
    input order. Lets create one more set of all prime numbers less than
    10
    p10 = set([2,3,5,7])
    print p10.
    
    To get union of these two sets we use '|' operator
    f10 | p10
    
    For intersection & operator is used:
    f10 & p10
    
    f10 - p10 gives difference between f10 and p10, which is, elements
    present in f10 but not present in p10.
    ^ operator gives us symmetric difference that is p10 union f10 minus
    f10 intersection p10
    f10 ^ p10

    To check if a set is super set or subset greater than and lesser than
    operators can be used
    set([2,3]) < p10
    returns True as p10 is superset of given set
    
    Similar to lists and dictionaries sets also supports containership so
    2 in p10
    returns True as 2 is part of set p10 and 
    4 in p10
    returns False.
    
    len function works with sets also:
    len(f10) returns the length, that is 5
    We can also use 'for' loops to iterate through a set.
    
    With this we come to the end of this tutorial on Dictionaries and 
    sets. We have covered some of properties of both data types and 
    functions supported by them. Thank you.

*** Notes