Dictionaries in Python

Dictionaries contain key:value pairs. Which means a collection of tuples with an attribute name and an assigned value to it. The semicolon present in between each key and values and attribute with values are delimited with a comma.  In python we can define dictionaries using dictionary construct.
First of all we need to define a dictionary:
Syntax:

<Name of the Dictionary >= {<key1> : <Value1> , <key2> : <Value2>,...., <key n> : <Value n> }
                      

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From the above syntax the value can be integer may not be enclosed by single/double quotes and separated by commas.
Example:
 

>>> COURSE ={'ORACLE': 1 ,'LINUX' : 2, 'SHELL' : 3 ,'PERL' : 4 }
                      >>> type(COURSE)
                      <type 'dict'>
                      

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The dictionaries are also case sensitive. We can access the above dictionary as like below:
 

>>> COURSE
                      {'ORACLE': 1, 'PERL': 4, 'SHELL': 3, 'LINUX': 2}
                      

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This will display the key and values within the dictionary, this are not ordered and if we want the dictionary to be in order then we have to sort it by values as the each key can be unique.
If we want to display the value specifically then we can call the dictionary by each key as like below:
 

>>> COURSE ['PERL']
                      4
                      

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Now if we want to add another element let say ‘PYTHON’ as value 4 then use as below:
 

>>> COURSE ['PYTHON']  = 4
                      >>> COURSE
                      {'ORACLE': 1, 'PERL': 4, 'PYTHON': 4, 'SHELL': 3, 'LINUX': 2}
                      >>> 
                      

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Now if I want to change the value of the key Linux then we have to use as like below:

>>> COURSE ['PYTHON']  = 9
                      >>> COURSE
                      {'ORACLE': 1, 'PERL': 4, 'PYTHON': 9, 'SHELL': 3, 'LINUX': 2}
                      >>> 
                      

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If we want to display the keys and values of a dictionary then we have to execute the name of the dictionary with key or values as like below:
 

>>> COURSE.keys()
                      ['ORACLE', 'PERL', 'PYTHON', 'SHELL', 'LINUX']
                      >>> COURSE.values()
                      [1, 4, 9, 3, 2]
                      

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For deleting the key value pair from the dictionary created then we have to use :

 
                      >>> del COURSE['PERL']
                      >>> COURSE
                      {'ORACLE': 1, 'PYTHON': 9, 'SHELL': 3, 'LINUX': 2}
                      >>> 
                       
                      

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Now we can see that the element PERL is deleted from the dictionary.
Let us see how we can loop the dictionary values:
 

>>> for key,val in COURSE.iteritems():
                                      print key,val
                       
                                     
                      ORACLE 1
                      PYTHON 9
                      SHELL 3
                      LINUX 2
                      >>> 
                      

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 For more information on dictionaries please visit :
https://www.python.org/doc/