Python Dictionary

 

Python Dictionary

       Python dictionary is an unordered collection of iteam.

Syntax

    key : value pair

 

How to create a dictionary ?

empty dictionary

my_dict = {}

dictionary with integer keys

my_dict = {1: 'One', 2: 'two'}

dictionary with mixed keys 

my_dict = {'name': 'Arun',1:'semester','marks': [45,67,89]}

using dict()

my_dict = dict({1: 'One', 2:'Two'})

from sequence having each item as a pair

my_dict = dict([(1,'One'), (2,'Two')])

 

How to access elements from a dictionary?

 

my_dict = {'name':'Ram', 'age': 26}

print(my_dict['name'])

print(my_dict.get('age'))

 

output

Ram

26

 

How to change or add element in a dictionary?

 

my_dict = {'name':'Ram', 'age': 26}

 

update value

my_dict['age'] = 27

print(my_dict)

my_dict['address'] = 'Madurai'

print(my_dict)                               

 

output

{'name':'Ram', 'age': 27}

{'name':'Ram', 'age': 27, 'address': 'madurai'}

 

How to delete or remove element from a

dictionary ?

 

create a dictionary

squares = { 1:1, 2:4, 3:9, 4:16, 5:25}

print(squares.pop(4))

remove a particular item

Output: 16

print(squares)

 

Output: { 1: 1, 2: 4, 3: 9, 5: 25}

print (squares.popitem())  

Output: (1, 1)

print (squares)

Output: {2: 4, 3: 9, 5: 25}

del squares[5]

print(squares)

Output:{2: 4, 3: 9}

 

 

squares.clear()

print(squares)

Output: {}

 

del squares

print(squares)

 #Throws Error

OUTPUT

16

{ 1: 1, 2: 4, 3: 9, 5: 25}

(1, 1)

{2: 4, 3: 9, 5: 25}

{2: 4, 3: 9}

{}

 

Python Dictionary Methods

Method	Dictionary
clear()	Remove all items from the dictionary.
copy()	Return a shallow copy of the dictionary.
fromkeys(seq[, v])	Return a new dictionary with keys from seq and value equal to v (defaults to none).
get(key[,d])	Return the value of key. if key dosenot exit, return d(defaluts to none).
items()	Return a new view of the dictionary's items(key, value)
keys()	Return a new view of the dictionary's keys.
pop(key[,d])	Remove the item  with key and return its value or d if key is not found. if d is not provided and key is not found, raises keyerror.
popitem()	Remove and return an arbitary item (key, value). raises keyerror If the dictionary is empty.
setdefault(key[,d])	If key is in the dictionary, return its value. if not, insert key with a value of d and return d (defaluts to none).
update([other])	Update the dictionary with the key/value pairs from other, overwriting existing keys.
values()	Return a new view of the dictionary's values

 

marks = {}.fromkeys(['math','english','science'], 0)

print(marks)

Output: {'English': 0, 'math': 0, 'science': 0}

for item in marks.item():

   print(item)

list(sorted(marks.keys()))

Output:

('science', 0)

('math', 0)

('english', 0)]

 

Python Dictionary Comprehension

 

squares = {x: x*x for x in range(6)}

print(squares)

 

Output:

{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

Other Dictionary Operations

Dictionary Membership Test

num_squares = {1: 1, 3: 9, 5: 25, 7: 49, 9: 81}

print(1 in num_squares)  output:true

print(2 not in num_squares)  output:true

 

print(49 in num_squares)       output:false

lterating Through a Dictionary

Using for loop we can iterate though eeach key in a dictionary

cubes = {1: 1, 2: 8, 3: 27, 4: 64, 5: 125}

for i in cubes :

    print (cubes[i])

 

OUTPUT

1

8

27

64

125

function	Description
all()	Return true if all keys of the dictionary are true (or if the dictionary empty)
any()	Return true if all key of the dictionary is true. if the dictionary is empty return false
len()	Return the length (the number of items) in the dictionary
cmp()	Compares items of two dictionaries
sorted()	Return a new sorted list of keys in the dictionary

 

Built - in method

 

> > > dict2 = {'country': 'india','code':91 }

> > > dict2.has_key('country')

1

> > >

> > > dict2['country']

'india'

> > >

> > > dict2.has_key('number')

0

 

> > > dict2.keys()

['country', 'code']

> > >

> > > dict2.values()

[91, 'india']

> > >

> > > dict2.items()

(['code',91), ('country', 'india')]

> > >

> > > for eachkey in dict2.keys():

... print 'dict2 key', eachkey, 'has valus',

dict2[eachkey]

...

 

> > > dict2keys = dict2.keys()

> > > dict2keys.sort()

> > > for eachkey in dict2keys:

...    print 'dict2 key', eachkey, 'has value',

dict2 [eachkey]

...

dict2 key country has value india

dict2 key code has value 91