Dictionary

# Creating a Dictionary   

d = {1: ‘One', 2: ‘Two', 3: ‘Three'}

b={"name" :"ajay","class":"11","rollno":25}

# Creating an empty Dictionary

Dict = {} 

# Creating a Dictionary  with dict() method

a = dict()

b=dict(d)

#access value of given key

>>> d['name']

'ajay'

>>> d['rollno']

25 

>>>d[1]

One

#access value of given key sing get() method

>>> d.get('name')

'ajay’

# change value of given key

>>> d['name']='harshit'

>>> d

{'name': 'harshit', 'class': '11', 'rollno': 25}

Add new item in Dictionary

We can easily add new element in dictionary by the following way

A = {1 : "One", 2 : "Two", 3 : "Three"}

A[4] = "Four"

print(A)

OUTPUT

{1 : "One", 2 : "Two", 3 : "Three", 4 : "Four"} 

#update() 

appends the key-value pair of the dictionary passed as the argument to the key-value pair of the given dictionary.

>>> dict1 = {'Mohan':95, 'Ram':89,'Suhel':92, 'Sangeeta':85}

>>> dict2 = {'Sohan':79,'Geeta':89}

>>> dict1.update(dict2)

>>> dict1

{'Mohan': 95, 'Ram': 89, 'Suhel': 92,'Sangeeta': 85, 'Sohan': 79, 'Geeta':89}

>>> dict2

{'Sohan': 79, 'Geeta': 89}

>>> car = {

  "brand": "Ford",

  "model": "Mustang",

  "year": 1964

              }

>>> car.update({"color":"white"})

>>> car

{'brand': 'Ford', 'model': 'Mustang', 'year': 1964, 'color': 'white’}

>>> car.update({"color":"blue","type":"petrol"})

>>> car

{'brand': 'Ford', 'model': 'Mustang', 'year': 1964, 'color': 'blue', 'type': 'petrol'}

We can also join two dictionaries into one by using update() method. It merge the keys and values of one dictionary into other and overwrites the values of the same key.

A = {1 : "One", 2 : "Two", 3 : "Three"}

B = {1: 'Amit', 2: 'Sunil', 5: 'Lata', 6: 'Suman', 7: 'Ravi'}

A.update(B)

print(A)

OUTPUT

{1: 'Amit', 2: 'Sunil', 3: 'Three', 5: 'Lata', 6: 'Suman', 7: 'Ravi'}

#It over writes the values of same keys and add the values of different keys

Removing an element from a Dictionary

There are two ways by which we can delete the elements of dictionary:

1.By using del statement :

Syntax of using del statement is : del <dictionary-name>[key of element]

B = {1: 'Amit', 2: 'Sunil', 5: 'Lata', 6: 'Suman', 7: 'Ravi'}

del B[2] # It will remove the element of key 2

print(B)

OUTPUT:

{1: 'Amit', 5: 'Lata', 6: 'Suman', 7: 'Ravi'}

B = {1: 'Amit', 2: 'Sunil', 5: 'Lata', 6: 'Suman', 7: 'Ravi'}

del B[3]  # It will return an error (KeyError) if the key given is not present in the dictionary

print(B)

OUTPUT:

KeyError

2. By Using pop() function :

This function not only delete the element of required key but also return the deleted value.

B = {1: 'Amit', 2: 'Sunil', 5: 'Lata', 6: 'Suman', 7: 'Ravi'}

a=B.pop(2) #It returns the element of Key - 2

print(a)

print(B)

OUTPUT

Sunil

{1: 'Amit', 5: 'Lata', 6: 'Suman', 7: 'Ravi'}

3 By using popitem() function

The popitem() method removes the item that was last inserted into the dictionary.

The removed item is the return value of the popitem() method, as a tuple, see example below.

d={1: 'one', 2: 'two', 3:'three’}

print(d)# delete top or last item from dictionary d.popitem()

print(d)

output

{1: 'one', 2: 'two', 3: 'three'}

{1: 'one', 2: 'two'}

The clear() method

removes all items from the dictionary.

Syntax: dict.clear()

d={1: 'one', 2: 'two', 3:'three’}

print(d)# remove all items from dictionary

d.clear()print(d)

# traversing  in dictionary(only traverse in keys)

>>> for i in d: 

  print(i)

name

class

rollno

# traverse in dictionary values

>>> for i in d:

  print(d[i])

harshit

11

25 

Write a program to enter roll number and names of five students and store the data in dictionary.

d = { }

for i in range(5):

  rno=int(input("Enter roll number"))

     name=input("Enter name of student")

  d[rno] = name

print(d)

What is the use of copy() method ?

They copy() method returns a copy (shallow copy) of the dictionary.

original = {1:'one', 2:'two'}

new = original.copy()

print('Orignal: ', original)

print('New: ', new)

What is the use of fromkeys() method ?

fromkeys() method returns a dictionary with the specified keys and the specified value.

Syntax

dict.fromkeys(keys, value)

Parameter  Description

keys     Required. An iterable specifying the keys of   the new dictionary

value   Optional. The value for all keys. Default   value is None

x = ('key1', 'key2', 'key3')

y = 0

thisdict = dict.fromkeys(x, y)

print(thisdict)

Ouput:

['key1': 0, 'key2': 0, 'key3': 0]

Another example

x = ('key1', 'key2', 'key3')

thisdict = dict.fromkeys(x)

print(thisdict)

Output:

['key1': None, 'key2': None, 'key3': None]

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

car = {

  "brand": "Ford",

  "model": "Mustang",

  "year": 1964

}

x = car.setdefault("color", "White")

print(x)

Output

White