Understanding Python Dictionary

In Python, dictionaries are associative arrays which store values in the form of 'key' and 'value' pair. Dictionaries are completely different from list and tuples as they are automatically indexed and only values are provided by the user.

But in the dictionary, we can provide both key and value. which means we can alter, modify and delete dictionary and its key, values.

Example : To creating empty dictonary use {} or we can use dictonary constructor 'dict()'.

d = {}
di = dict()

print(d)
print(di)

#PYTHON OUTPUT
{}
{}

Example: To add values in dictionary

d = {
    'user_id' : 1,
    'username' : 'Jake',
    'age' : 25,
    'salary' : 95000.75,
}

di = dict(
    user_id=2,
    username='Sushant',
    age=29,
    salary=105000.50
)

print('Dictonary using curly brackets')
print(d)

print('n') #next line

print('Dictonary using dict constructor')
print(di)

#PYTHON OUTPUT
Dictonary using curly brackets
{'user_id': 1, 'username': 'Jake', 'age': 25, 'salary': 95000.75}


Dictonary using dict constructor
{'user_id': 2, 'username': 'Sushant', 'age': 29, 'salary': 105000.5}

Example: Values from dictionary can be accessed using keys or by get() method

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}
print(d['username'])
print(d.get('username'))

#PYTHON OUTPUT
Jake
Jake

Example: Updating values in dictionary.

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

d['username']='Rohit'

print(d['username'])

#PYTHON OUTPUT
Rohit

Appending new item in dictionary can be achieved by simply giving the name of key and value and it will be added in the bottom of dictionary.

Syntax:

dict['key'] = 'value'

Example

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

d['date_of_birth'] = '1990-03-22'

print(d)

#PYTHON OUTPUT
{'user_id': 1, 'username': 'Jake', 'age': 25, 'salary': 95000.75, 'date_of_birth': '1990-03-22'}

There are various method to remove a item from dictionary

• Use del keyword by calling dictionary with a key name to delete. This will delete the item completely.
• Use pop() method by specifying key name inside parentheses.

Syntax

dict.pop('key_name')

• Use popitem() this will remove the last key and value from Dictionary.

Syntax

dict.popitem()

Example

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

del d['username'] #key 'username' will be removed from dictonary

print(d)

#PYTHON OUTPUT
{'user_id': 1, 'age': 25, 'salary': 95000.75}

Example : remove use pop() method.

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

d.pop('username')
print(d)

#PYTHON OUTPUT
{'user_id': 1, 'age': 25, 'salary': 95000.75}

Example : remove using 'popitem()' method.

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

d.popitem() #this method will remove the last item from dictonary in this case it is 'salary'
print(d)

#PYTHON OUTPUT
{'user_id': 1, 'username': 'Jake', 'age': 25}

To empty dictonary use clear() method.

Syntax

dict.clear()

Example

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

d.clear()
print(d)

#PYTHON OUTPUT
{} #we get the empty dictonary

To delete dictionary completely use del keyword before dictionary variable.

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

del d
print(d)

#PYTHON ERROR OUTPUT
NameError: name 'd' is not defined #because we have deleted the dictonary

Check if a key exists in dictionary

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

if 'username' in d:
    print('Exits')
else:
    print('Does not exits')

#PYTHON OUTPUT
Exits

To check if a given value exists in dictionary use values() method.

Example

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

if 'Jake' in d.values():
    print('Exits')
else:
    print('Does not exits')

#PYTHON OUTPUT
Exits

Example: To count the number of items present in dictionary use len() method.

d = {
'user_id' : 1,
'username' : 'Jake',
'age' : 25,
'salary' : 95000.75,
}

print(len(d))

#PYTHON OUTPUT
4

This article was taken from Working with Dictionary in Python