The document provides a comprehensive overview of dictionaries in Python, detailing their structure as key-value pairs, how to access and manipulate them, and various built-in methods available for dictionary operations. Key concepts include creating dictionaries, adding, modifying, deleting items, and using methods like clear(), copy(), get(), items(), keys(), pop(), and update(). Examples illustrate syntax and expected outputs for each operation.

1. 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.  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.
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3.  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.
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4.  Style 1:
stud={'rollno':1,'name':'Soham','class':'FY’}
 Style 2: More readable format
stud={'rollno':1,
'name':'Soham',
'class':'FY'}
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5. stud={'rollno':1,
'name':'Soham',
'class':'FY'}
print(stud)
Output:
{'rollno': 1, 'name': 'Soham', 'class': 'FY'}
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6.  To access values in dictionary, use square brackets along with key.
 We can access value/data using key only.
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7. 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
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8. 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'}
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9. 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'}
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10.  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'}
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11. 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/Pyth
on312/sam1.py", line 10, in <module>
print(f'Dictionary after deleting stud dictionary
{stud}')
NameError: name 'stud' is not defined
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12. 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
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13.  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'}
{}
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14.  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'}
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15.  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
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16.  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')])
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17.  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')])
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18.  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'])
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19.  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'])
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20.  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
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21.  The popitem() 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'}
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22.  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'}
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23.  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'])
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24.  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'])
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25.  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'}
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26.  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'}
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