Termwise

Syllabus
2021-22

Chapter 14
Dictionary

Computer Science
Class XI ( As per CBSE Board)
 Dictionary

It is an unordered collection of items where each

item consist of a key and a value.
It is mutable (can modify its contents ) but Key must
be unique and immutable.
 Dictionary
Creating A Dictionary
It is enclosed in curly braces {} and each item is separated from other item by a
comma(,). Within each item, key and value are separated by a colon (:).Passing
value in dictionary at declaration is dictionary initialization.get() method is used to
access value of a key
e.g.
dict = {‘Subject': ‘Informatic Practices', 'Class': ‘11'}

Accessing List Item

dict = {'Subject': 'Informatics Practices', 'Class': 11}
print(dict)
print ("Subject : ", dict['Subject'])
print ("Class : ", dict.get('Class'))
OUTPUT
{'Class': '11', 'Subject': 'Informatics Practices'}
('Subject : ', 'Informatics Practices')
('Class : ', 11)
 Dictionary
Iterating / Traversing through A Dictionary
Following example will show how dictionary items can be accessed through loop.
e.g.
dict = {'Subject': 'Informatics Practices', 'Class': 11}
for i in dict:
print(dict[i])
OUTPUT
11
Informatics Practices
Updating/Manipulating Dictionary Elements
We can change the individual element of dictionary.
e.g.
dict = {'Subject': 'Informatics Practices', 'Class': 11}
dict['Subject']='computer science'
print(dict)
OUTPUT
{'Class': 11, 'Subject': 'computer science'}
 Dictionary

Deleting Dictionary Elements

del, pop() and clear() statement are used to remove
elements from the dictionary.
del e.g.
dict = {'Subject': 'Informatics Practices', 'Class': 11}
print('before del', dict)
del dict['Class'] # delete single element
print('after item delete', dict)
del dict #delete whole dictionary
print('after dictionary delete', dict)

Output
('before del', {'Class': 11, 'Subject': 'Informatics Practices'})
('after item delete', {'Subject': 'Informatics Practices'})
('after dictionary delete', <type 'dict'>)
 Dictionary

pop() method is used to remove a particular item in a

dictionary. clear() method is used to remove all
elements from the dictionary.
e.g.
dict = {'Subject': 'Informatics Practices', 'Class': 11}
print('before del', dict)
dict.pop('Class')
print('after item delete', dict)
dict.clear()
print('after clear', dict)

Output
('before del', {'Class': 11, 'Subject': 'Informatics Practices'})
('after item delete', {'Subject': 'Informatics Practices'})
('after clear', {})
 Dictionary

Built-in Dictionary Functions

S.No. Function & Description
len(dict)Gives the total length of the dictionary. It is equal to
the number of items in the dictionary.
1 dict = {'Name': 'Aman', 'Age': 37};
print ("Length : %d" % len (dict))
OUTPUT ->2
str(dict)Return a printable string representation of a
2 dictionary

type(variable)If variable is dictionary, then it would return a

dictionary type.
3
 Dictionary

Built-in Dictionary Methods

S.No. Method & Description
dict() - creates dictionary
1 x = dict(name = “Aman", age = 37, country = “India")
Here x is created as dictionary
keys() - returns all the available keys
x = dict(name = “Aman", age = 37, country = “India")
2
print(x.keys())
OUTPUT->dict_keys(['country', 'age', 'name'])
values() - returns all the available values
x = dict(name = “Aman", age = 37, country = “India")
3
print(x.values())
OUTPUT->dict_values(['India', 37, 'Aman'])
 Dictionary

Built-in Dictionary Methods

S.No. Method & Description
items() - return the list with all dictionary keys with values.
x = dict(name = "Aman", age = 37, country = "India")
4
print(x.items())
OUTPUT->dict_items([('country', 'India'), ('age', 37), ('name', 'Aman')])
update()-used to change the values of a key and add new keys
x = dict(name = "Aman", age = 37, country = "India")
5 d1 = dict(age= 39)
x.update(d1,state="Rajasthan")
print(x)
OUTPUT-{'country': 'India', 'age': 39,'name':'Aman','state': 'Rajasthan'}
 Dictionary

Built-in Dictionary Methods

S.No. Method & Description
del -used to remove key
x = dict(name = "Aman", age = 37, country = "India")
del x['age']
6
print(x)
OUTPUT->{'country': 'India', 'name': 'Aman'}
del x -> will remove complete dictionary
fromkeys() – is used to create dictionary from keys
keys = {'a', 'e', 'i', 'o', 'u' }
value ="Vowel"
7
vowels = dict.fromkeys(keys, value)
print(vowels)
OUTPUT-> {'i': 'Vowel', 'u': 'Vowel', 'e': 'Vowel', 'a': 'Vowel', 'o': 'Vowel'}
 Dictionary

Built-in Dictionary Methods

S.No. Method & Description
copy() - returns a shallow copy of the dictionary.
x = dict(name = "Aman", age = 37, country = "India")
y=x.copy()
print(y)
8 print(id(x))
print(id(y))
OUTPUT - >{'country': 'India', 'age': 37, 'name': 'Aman'}
33047872
33047440
popitem() – removes last item from dictionary
x = dict(name = "Aman", age = 37, country = "India")
9 x.popitem()
print(x)
OUTPUT-> {'age': 37, 'name': 'Aman'}
 Dictionary

Built-in Dictionary Methods

S.No. Method & Description
setdefault() method returns the value of the item with the specified key.
If the key does not exist, insert the key, with the specified value.
x = dict(name = "Aman", country = "India")
10
y=x.setdefault('age',39)
print(y)
OUTPUT-> 39
max() – returns key having maximum value
Tv = {'a':100, 'b':1292, 'c' : 88}
11 Keymax = max(Tv, key=Tv.get)
print(Keymax)
OUTPUT-> b
12 min()- returns key having minimum value
 Dictionary

Built-in Dictionary Methods

S.No. Method & Description
sorted- sort by key or value
dict1 = {'b':100, 'a':12, 'c' : 88}
13 y = sorted(dict1.items(),key=lambda x: x[1],reverse=True)
print(y)
OUTPUT-> [('b', 100), ('c', 88), ('a', 12)]
 Dictionary

count the number of times a character appears in agiven

string using a dictionary
input_string = "python.mykvs.in"
frequencies = {}
for char in input_string:
if char in frequencies:
frequencies[char] += 1
else:
frequencies[char] = 1
print ("Per char frequency in '{}' is :\n {}".format(input_string,
str(frequencies)))
OUTPUT
Per char frequency in 'python.mykvs.in' is :
{'i': 1, 'h': 1, 'k': 1, 'm': 1, 'o': 1, 'n': 2, 'p': 1, 's': 1, 't': 1, 'v': 1, 'y': 2, '.': 2}
 Dictionary

create a dictionary with names of employees, their

salary and access them
employees =
{'Aman':{'salary':'10000'},'Mayur':{'salary':'51000'}}
employee1 = employees['Aman']
print(employee1)

OUTPUT
{'salary': '10000'}
 Dictionary

Questions.
1. Create dictionary to store 4 student details with
rollno,name,age field.Search student in list.
2. Create dictionary for month and noofdays for a
year. User is asked to enter month name and
system will show no of days of that month.