Mutable objects : Dictionary (Dict)

Objects of type dict are like lists except that "indices " need not be integers , they can be values of any immutable types . Since they are not ordered, the indices are referred as keys.  Dictionaries can be thought of a key/value pairs where each key has a corresponding value. Literals of type dict are enclosed in curly braces and each element is written as a key followed by a colon followed by a value. Each key value pair is seperated by a comma.

For example:

>>>d  = {1:red, 2:blue, 3:yellow , 4: orange, 5:black, 6: white}

>>>print d[1]

>>>red

Keys are unique within a dictionary while values may not be. The values of a dictionary can be of any type, but the keys must be of immutable data type such as strings ,numbers, or tuples.


Operators on Dictionaries:

lend(d)  :  returns the number of stored entries i.e. the number of key/value pairs

del d[k]  : deletes the key k together with its value

k in d     :  True if a key k exists in dictionary d

k not in d : True if a key deosn't exists in dictionary d

Methods on Dictionaries

1. Iterating over dictionary
    for key in d:
        print key 

2. dict.setdefault(key,default=None)
    will set dict[key] = default if key not in dict

3. dict.clear()
    removes all elements of dictionary dict

4. dict.copy
    returns a copy of dictionary dict

5. dict.items()
    returns a list of dict's(key,value) pairs

6.dict.keys()
    returns a list of keys

7.dict.values()
    returns a list of values