Unit4-Basic Concepts and methods of Dictionary.pptx

Refer this to understand Dictionary data structure

1. Dictionary By, Prof. S.S.Gawali Computer Engineering, Sanjivani College of Engineering Sanjivani Rural Education Society’s Sanjivani College of Engineering, Kopargaon-423 603 Department of Computer Engineering

2. What is Dictionary? Dictionary is mapping data type in python. Dictionary is a data structure which store values as a pair of key and value. In dictionary keys are unique and immutable. In dictionary values are not unique but mutable. Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 2

3. How to create Dictionary Dictionary consist item as pair of key and value. Dictionary is represented by {} Each key and value is separated by : Each item separated by , Syntax: dict ={'a':1,'b':2,'c’:3} Here dict is variable to store dictionary data. ‘ a’,’b ’ and ‘c’ are keys 1,2 and 3 are values of keys. Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 3

4. How to create Dictionary? Style 1: stud={'rollno':1,'name':'Soham','class':'FY’} Style 2: More readable format stud={'rollno':1, ' name':'Soham ', ' class':'FY '} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 4

5. Program to Create and Display Dictionary Data stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print(stud) Output: {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 5

6. How to access Values in Dictionary? To access values in dictionary, use square brackets along with key. We can access value/data using key only. Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 6

7. Program to access value in dictionary stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print(stud[' rollno ']) #Display rollno value print(stud['name']) #Display name value print(stud['class']) #Display class value print( f'Name of Student is {stud['name']}')# display value with message Output: 1 Soham FY Name of Student is Soham Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 7

8. Add item in the dictionary using key stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print( f'Dictionary {stud}') stud['Div']='G' #add new key and value print( f'Dictionary after adding new item {stud}’) [note: new item added at the end] Output: Dictionary {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} Dictionary after adding new item {' rollno ': 1, 'name': 'Soham', 'class': 'FY', 'Div': 'G'} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 8

9. Modify Item in Dictionary stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print( f'Dictionary before modification {stud}’) stud[' rollno ']=2 #modify rollno key’s value print( f'Dictionary after modification {stud}') Output: Dictionary before modification {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} Dictionary after modification {' rollno ': 2, 'name': 'Soham', 'class': 'FY'} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 9

10. Delete operation del statement use to delete item or delete dictionary in python. stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print( f'Dictionary {stud}’) del stud['name'] # deleting key name and its value print( f'Dictionary after delete operation {stud}’) Output: Dictionary {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} Dictionary after delete operation {' rollno ': 1, 'class': 'FY'} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 10

11. Deleting dictionary stud={'rollno':1, ' name':'Soham ', ' class':'FY ’} print( f'Dictionary {stud}')# display value with message del stud # delete stud dictionary print( f'Dictionary after deleting stud dictionary {stud}') Output: Dictionary {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} Traceback (most recent call last): File "C:/Users/DELL/AppData/Local/Programs/Python/Python312/sam1.py", line 10, in <module> print( f'Dictionary after deleting stud dictionary {stud}') NameError : name 'stud' is not defined Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 11

12. Dictionary Methods Method Description clear() Removes all the elements from the dictionary copy() Returns a copy of the dictionary get() Returns the value of the specified key items() Returns a list containing a tuple for each key value pair keys() Returns a list containing the dictionary's keys pop() Removes the element with the specified key popitem() Removes the last inserted key-value pair update() Updates the dictionary with the specified key-value pairs values() Returns a list of all the values in the dictionary Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 12

13. clear() The clear() used to remove all items from dictionary. Synatax dict.clear () Example stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print(stud) # display before clearing stud.clear () # clear stud dictionary print(stud) # display after clearing Output: {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} {} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 13

14. copy() The copy() used to copy dictionary content to new dictionary. Syntax: dict.copy () Example stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print(stud) # display stud data detail= stud.copy () # copy stud dictionary data to detail print(detail) # display detail data Output: {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 14

15. get() The get() used to return the value for the given key if present in the dictionary. If not, then it will return None (if get() is used with only one argument). Syntax: dict.get ( key,default_value ) Key: Required. The name of key which value you want to retrieve. Default_value : Optional. A value to return if the specified key do not exist. Example: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print( stud.get (' rollno '))#Display value of rollno key print( stud.get ('div'))#Display value of div key print( stud.get (' div','this key is not present’))#Display default value if key is not present Output 1 None this key is not present Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 15

16. items() The items() method is used to return the list with all dictionary keys with values. Syntax dict.items () Example 1: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print( stud.items ()) Output: dict_items ([(' rollno ', 1), ('name', 'Soham'), ('class', 'FY')]) Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 16

17. items() Example 2: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} item= stud.items () # item variable to stored items in stud dict print(' origional dictionary items') print(item) #display item del stud['class'] #deleting class key and its value print('updated dictionary items') print(item) #updated items in stud dictionary Output: origional dictionary items dict_items ([(' rollno ', 1), ('name', 'Soham'), ('class', 'FY')]) updated dictionary items dict_items ([(' rollno ', 1), ('name', 'Soham')]) Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 17

18. keys() The keys() method returns a view object. The view object contains the keys of the dictionary, as a list. Syntax: dict.keys () Example: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print( stud.keys ()) # display keys of stud dictionary as a list Output: dict_keys ([' rollno ', 'name', 'class']) Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 18

19. keys() Example 2: When an item is added in the dictionary, the view object also gets updated: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} key= stud.keys () # key variable to stored keys in stud dict print(' origional dictionary keys') print(key) #display keys stud['branch']='Comp' #inserting new branch key print('updated dictionary keys') print(key) #updated keys in stud dictionary Output: origional dictionary keys dict_keys ([' rollno ', 'name', 'class']) updated dictionary keys dict_keys ([' rollno ', 'name', 'class', 'branch']) Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 19

20. pop() The pop() used to remove the specific item from the dictionary. Syntax: dict.pop ( key,default_value ) Key: Required. The name of key which item you want to remove. Default_value : Optional. A value to return if the specified key do not exist. Example: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print( stud.pop ('name')) # print removed key's value print(stud) # display dictionary print( stud.pop (' branch','not available'))# print default value if key is not present in the dictionary Output: Soham {' rollno ': 1, 'class': 'FY'} not available Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 20

21. popitem (): The p opitem () method removes the item that was last inserted into the dictionary. It returns value as a tuple (key and its value). Syntax: dict.popitem () Example: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print( stud.popitem ())#remove and print last key and its value print( f'Updated Dictionary data {stud}') Output: ('class', 'FY') Updated Dictionary data {' rollno ': 1, 'name': 'Soham'} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 21

22. update() The update() method used to inserts the specified items to the dictionary. The specified items can be a dictionary, or an iterable object with key value pairs. Syntax: dict.update ( iterable ) Iterable is a dictionary or an iterable object with key value pairs, that will be inserted to the dictionary Example: stud={'rollno':1,'name':'Soham','class':'FY'} stud.update ({' branch':'comp '})# inserting new item print(stud) # display updated dictionary d={' name':'Om '} # new dictionary stud.update (d) # updating name key using d dict print(stud) # display updated dictionary stud.update (div=' G',prn ='123')# updating using iterable print(stud) # display updated dictionary Output: {' rollno ': 1, 'name': 'Soham', 'class': 'FY', 'branch': 'comp'} {' rollno ': 1, 'name': 'Om', 'class': 'FY', 'branch': 'comp'} {' rollno ': 1, 'name': 'Om', 'class': 'FY', 'branch': 'comp', 'div': 'G', 'prn': '123'} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 22

23. values() The values() method returns a view object. The view object contains the values of the dictionary, as a list. Syntax: dict.values () Example: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} print( stud.values ()) # display keys of stud dictionary as a list Output: dict_values ([1, 'Soham', 'FY']) Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 23

24. values() Example 2: When an item is added in the dictionary, the view object also gets updated: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} val = stud.values () # val variable to stored keys in stud dict print(' origional dictionary values') print( val ) #display values stud['branch']='Comp' #inserting new branch key print('updated dictionary values') print( val ) #updated values in stud dictionary Output: origional dictionary values dict_values ([1, 'Soham', 'FY']) updated dictionary values dict_values ([1, 'Soham', 'FY', 'Comp']) Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 24

25. Aliasing with Dictionaries An Aliasing Dictionary is use to assign a dictionary to another dictionary by updating the content on both dictionary at a time. Aliasing is whenever two variables refer to the same dictionary object, changes to one affect the other Example: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} stud_new ={} #another dict stud_new =stud # aliasing stud dict to stud_new print( stud_new ) # diplay stud_new dict stud['class']='SY' #updating stud dict print( f'Original Dict : {stud}')# display stud dict print( f'Alised Dict : { stud_new }')# display stud_new dict Output: {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} Original Dict : {' rollno ': 1, 'name': 'Soham', 'class': 'SY'} Alised Dict : {' rollno ': 1, 'name': 'Soham', 'class': 'SY'} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 25

26. Copying with dictionary Copy() used to copy dictionary. But with this updating one dictionary not reflected on another dictionary. Example: stud={'rollno':1, ' name':'Soham ', ' class':'FY '} stud_new ={} #another dict stud_new = stud.copy () # copying stud dict to stud_new print( stud_new ) # diplay stud_new dict stud['class']='SY' #updating stud dict print( f'Original Dict : {stud}')# display stud dict print( f'Copied Dict : { stud_new }')# display stud_new dict Output: {' rollno ': 1, 'name': 'Soham', 'class': 'FY'} Original Dict : {' rollno ': 1, 'name': 'Soham', 'class': 'SY'} Alised Dict : {' rollno ': 1, 'name': 'Soham', 'class': ‘FY'} Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 26

27. Thank You…. Department of Computer Engineering, Sanjivani College of Engineering, Kopargaon 27