Class 11 Python basic data type Dictionary (dict{}

1. DICTIONARY
• WHAT IS DICTIONARY?
• HOW TO CREATE DICTIONARY?
• HOW TO ACCESS / TRAVERSE ELEMENTS IN DICTIONARY?
• DICTIONARY OPERATIONS
• DICTIONARY FUNCTIONS

2. WHAT IS DICTIONARY?
• It is unordered collection of elements in the form key:value pair.
• Keys must be of immutable type such as string,number or a
tuple.
• Values can be of any type.
• It is Mutable.
• Indexed by keys not by Numbers.
• Keys must be unique.
• Dictionaries are also called ‘associative arrays’ or ‘mappings’ or
hashes.
• Examples:
• D1 = { }
• Signal = {‘Red’:1, ‘Green’:2, ‘Yellow’:3}
• Dict1={1:’test’, ‘string’: 2, ‘list’:[1,2,3], (5,7):’tuple’}

3. How to create Dictionary?
1) Initialisation
Signal = {‘Red’:1, ‘Green’:2, ‘Yellow’:3}
2) Using dict( )
1) D = dict( )  Creates Empty dictionary
2) Signal = dict(Red=1,Green=2, Yellow=3)
3) Signal = dict([‘Red’,1],[‘Green’,2],[‘Yellow’,3])
4) Signal = dict(zip((‘Red’,’Green’,’Yellow’),(1,2,3)))

4. HOW TO ACCESS ELEMENTS IN A DICTIONARY?
• In Dictionary, the elements are accessed through keys.
Syntax: <DictionaryName>[<key>]
Months={‘Jan’:31,’Feb’:28,’Mar’:31,’Apr’:30,’May’:31}
Vowels={1:’a’, 2:’e’, 3:’i’, 4:’o’, 5:’u’}
>>>Months[‘Feb’]
28
>>>Months[‘May’]
31
>>>Vowels[3]
I
>>>Vowels[‘e’]
Error Message

5. Traversing a Dictionary
Syntax:
for <item> in <Dictionary> :
item Keys in dictionary
Dictionary[item]  Value corresponding to key
Ex:1
D1={‘Red’:1, ‘Green’:2, ‘Yellow’:3}
for key in D1:
print(key, D1[key])
Output:
Red 1
Green 2
Yellow 3
for i in D1:
print(D1[i])
Output: Output:
1 2
2 1
3 3
Dictionaries are unordered set of
elements, the printed order of elements
is not same as the order you store the
elements in.

6. CHARACTERISTICS OF A DICTIONARY
1. Unordered Set
2. Not a sequence
3. Indexed by keys not by Numbers
4. Keys must be unique
5. Mutable
6. Internally stored as Mappings

7. Dictionary Operations
Student={‘Name’:’John’, ‘Age’:16}
1) Adding Elements to Dictionary
Syntax: Dictionary[key] = value
>>> Student[‘Class’]=12
>>> Student
{‘Name’:’John’, ‘Age’:16,’Class’:12}
2) Updating Existing elements
Syntax: Dictionary[key]=Newvalue
Ex: Student[‘Age’]=17
Result: Student={‘Name’:’John’, ‘Age’:17}
Student[‘age’]=18
Result: : Student={‘Name’:’John’, ‘Age’:17, ‘age’:18}

8. 3) Deleting Elements from Dictionay
i) Using del statement
Syntax: del dictionary[key]
>>>del Student[‘age’]
>>>del Student
>>>del Student[‘DOB’]
Error Message : KeyError: 'DOB‘
ii) Using pop( ) method
Syntax: <Dictionary>.pop(<key>)
>>>Student.pop(‘Age’)
16

9. 4) Checking for Existence of a Key
Use membership operator in and not in
<key> in <Dictionary)
Returns True if the given key is present
<key> not in <Dictionary>
 Returns True if the given key is not present
Ex:
>>>’Age’ in Student
True
>>>’DOB’ not in Student
True

10. Dictionary Functions and Methods
Student = {‘Name’:’John’, ‘Age’:16, ‘Class’:12}
1) len( )  Returns no of elements in a dictionary
Syntax: len(<dictionary>)
Argument: 1 argument of type Dictionary
Return: Integer
Example: >>> len(Student)
3
2) clear( )  Clears/Deletes all elements in a dictionary
Syntax: <dictionary>.clear( )
Argument: No argument
Return: Nothing
Example: >>>Student.clear( )
>>> Student
{ }

11. 3) get( )  Get the item with given key or User defined message
Syntax: <dictionry>.get(key , [default])
Argument: 1 – Essential argument, 1 – Optional argument
Return: Object/ Value
Example: >>> Student.get(‘Name’)
John
>>>Student.Get(‘dob’, “Key does not exist”)
Key does not exist
4) items( )  Returns all the items in the dictionary as (key,value) tuple
Syntax: <dictionary>.items( )
Argument: No argument
Return: Sequence of (key, value) pair
Example: >>>Student.items( )
dict_items([('Name', 'John'), ('Age', 17), ('Class', 12)])

12. 5) keys( )  Returns all the keys in dictionary as a list.
Syntax: <dictionary>.keys( )
Argument: No argument
Return: List of keys
Example: >>> Student.keys( )
[‘Name’, ‘Age’, ‘Class’]
6) values( )  Returns all the values in dictionary as a list.
Syntax: <dictionary>.values( )
Argument: No argument
Return: List of values
Example: >>> Student.values( )
[‘John’, 16,12]

13. 7) update( )  Merges key:value pair from new dictionary into the original
dictionary, adding or replacing as needed.
Syntax: <dictionary>.update(<dictionary>)
Argument: 1 argument of type dictionary
Return: Nothing
Example:>>> School ={‘name’:’vvs’, ‘board’:cbse}
>>>Student.update(School)
>>>Student
{‘Name’:’John’, ‘Age’:16,’Class’:12, ‘name’:’vvs’, ‘board’:cbse }
8) pop( )  Returns and deletes element from dictionary
Syntax: <dictionary>.pop(<key>)
Argument: 1 argument of key item
Return: Value of any type
Example: >>>Student. pop(‘Class’)
12
>>>Student
{‘Name’: ’John’, ‘Age’:16}

14. THANK YOU 