Dictionaries

Python dictionaries are kind of hash table type which consist of key-value pairs of unordered elements.

Keys: must be immutable data types ,usually numbers or strings.
Values: can be any arbitrary Python object.

Python Dictionaries are mutable objects that can change their values.

A dictionary is enclosed by curly braces ({}), the items are separated by commas, and each key is separated from its value by a colon (:).

Dictionary’s values can be assigned and accessed using square braces ([]) with a key to obtain its value.

Simple script to show dictionary usage:

dict1 = {'Name': 'Abolfazl', 'Age':23, 'Major': 'CSE'}

# Access dictionary data
print('name: ', dict1['Name'])
print('age: ', dict1['Age'])
print(dict1.keys())
print(dict1.values())
print(dict1.items())

# Update dictionary data
dict1['Age'] = 24
dict1['University'] = 'SBUK'
print('new age: ', dict1['Age'])
print('university: ', dict1['University'])

# Delete dictionary data
del dict1['Name']
print(dict1)
dict1.clear()
print(dict1)

Output:

name: Abolfazl
age: 23
dict_keys(['Name', 'Age', 'Major'])
dict_values(['Abolfazl', 23, 'CSE'])
dict_items([('Name', 'Abolfazl'), ('Age', 23), ('Major', 'CSE')])
new age: 24
university: SBUK
{'Age': 24, 'Major': 'CSE', 'University': 'SBUK'}
{}

Common Dictionary Methods

Method	Description
`dict.keys()`	Returns list of dict's keys
`dict.values()`	Returns list of dict's values
`dict.items()`	Returns a list of dict's (key, value) tuple pairs
`dict.get(key, default=None)`	For key, returns value or default if key not in dict
`dict.has_key(key)`	Returns `True` if key in dict, `False` otherwise
`dict.update(dict2)`	Adds dict2's key-values pairs to dict
`dict.clear()`	Removes all elements of dict

Common Dictionary Functions

Function	Description
`cmp(dict1, dict2)`	Compares elements of both dict.
`len(dict)`	Gives the total number of (key, value) pairs in the dictionary.