dictionary.org
changeset 128 fa5c77536e4e
parent 127 76fd286276f7
child 129 dcb9b50761eb
child 146 b92b4e7ecd7b
--- a/dictionary.org	Mon Sep 13 18:35:56 2010 +0530
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,126 +0,0 @@
-* Dictionaries
-*** Outline
-***** Dictionaries
-***** Sets
-***** Arsenal Required
-*** Script
-    Welcome friends. 
-    
-    In previous tutorial we covered Lists, Tuples and related 
-    functions. In this session we shall continue with Python
-    data structures and cover Dictionaries and sets. We have already 
-    covered some basics of Dictionaries in session on Statistics. Here
-    we shall revisit those concepts and some new ones. 
-    
-    We give it a name and it returns a corresponding number. 
-    Dictionaries are just key-value pair. For each 'key' there is
-    corresponding 'value' associated with it. In lists we use indexes 
-    to access elements, here we use the 'key'. 
-    
-    Lets start by opening IPython interpreter. 
-    '{}' are used to create Python dictionaries. Lets create a dictionary say
-
-    player = {'Mat': 134,'Inn': 233,
-    'Runs': 10823, 'Avg': 52.53}
-    Let's see what player contains by typing:
-
-    print player
-
-    Its a dictionary storing statistics of a cricket player.
-    Here 'Mat', 'Inn' etc are the keys. Now in order to get the 'average' of
-    this player we simply type
-    print player['Avg']
-    52.53
-
-    To add a new key-value pair to this dictionary we type
-    player['Name'] = 'Rahul Dravid'
-    print player
-    As you can see the given key-value pair has been added.
-    Please note that Python dictionaries don't maintain the order
-    in which the key-value pairs are stored. The order might change
-    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 the new one. So
-    print player
-    will have updated value
-
-    As we covered in one of previous sessions 'for' can be used to iterate
-    through lists. The same is possible in case of dictionaries too. We can
-    iterate over them using the 'keys', for example:
-    for key in player:
-        print key, player[key]
-    This prints the keys in the dictionary along with their corresponding 
-    values. Notice that the order is not the same as we entered it.
-    
-    We saw how containership works in lists. There we can check if a 
-    value is present in a list or not but in case of Dictionaries we
-    can only check for the containership of the 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 for a 'value' it will not work.
-    Dictionaries support functions to retrieve keys and values 
-    such as
-    player.keys()
-    returns the list of all 'keys'
-    player.values()
-    return list of all 'values'    
-
-    Now we shall move on to 'sets'. Sets in Python are an unordered 
-    collection of unique elements. This data structure comes in 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])
-    And thats how a set is created.
-    f10 is the set of Fibonacci numbers less than 10
-    lets print the value of f10
-    print f10
-
-    As we mentioned earlier, these are unordered structure so order of
-    elements is not maintained, and output order is different than 
-    input order, just as in dictionaries. Lets create one more set, a 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 the or '|' operator
-    f10 | p10
-    
-    For intersection we use the and '&' operator:
-    f10 & p10
-    
-    f10 - p10 gives difference between f10 and p10, that is, the set of all elements
-    present in f10 but not in p10.
-    The carat '^' operator gives us the symmetric difference of 2 sets. That is
-    f10 union p10 minus f10 intersection p10
-    f10 ^ p10
-
-    To check if a set is the super set or a subset of another set, the greater than 
-    and the lesser than operators are 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.
-    
-    The 'len' function works with sets also:
-    len(f10) returns the length, which is 5 in this case.
-    We can also use 'for' loops to iterate through a set just as with dictionaries and lists.
-    
-    With this we come to the end of this tutorial on Dictionaries and 
-    sets. We have seen how to initialize dictionaries, how to index them using keys
-    and a few functions supported by dictionaries. We then saw how to initialize
-    sets, perform various set operations and a few functions supported
-    by sets. Hope you have enjoyed it, Thank you.
-
-*** Notes