A dictionary in Python is equivalent to a Map object in Java
Dictionary features:

• Read by key instead of index
• A dictionary is an unordered collection of arbitrary objects
• Dictionaries are variable and can be nested arbitrarily
• Key in dictionary must be unique
  If the key appears twice, the latter value will be remembered
• Key in dictionary must be immutable
  Keys can use numbers, strings, tuples, not lists

Create and delete

dictionary = {'qq': '61553696', 'Blog': 'Hearing impaired old boy', 'Telephone': '8888888'}
print(dictionary)

"""Two ways to create an empty dictionary"""
dictionary = {}
dictionary1 = dict()

"""Existing data creation dictionary"""
# 1. Map function create dictionary
name = ['Zhang San', 'Li Si', 'Wang Wu']
age = ['19', '18', '17']
# The zip() function combines elements of multiple lists or tuples into tuples, and returns the zip object of these contents
dictionary = dict(zip(name, age))
print(dictionary)

# 2. Key value pair create dictionary
dictionary = dict(qq='61553696', Blog='Hearing impaired old boy', Telephone='8888888')
print(dictionary)

# Tuples and lists creating Dictionaries
name_tuple = ('Zhang San', 'Li Si', 'Wang Wu')
age = ['19', '18', '17']

dict1 = {name_tuple: age}
print(dict1)    # The result is: {('zhang San ',' Li Si ',' Wang Wu '): ['19', '18', '17']}

# Clear all elements of the dictionary, the source dictionary becomes empty
dict1.clear()
print(dict1)    # {}

# del command to delete the entire dictionary
del dict1
print(dict1)    # NameError: name 'dict1' is not defined

# The pop() method deletes and returns the element of the specified 'key'
# The popitem() method deletes and returns an element in the dictionary

Key value pair ACCESS Dictionary

# When getting the value of a specified key, an exception is thrown if the specified key does not exist
dictionary = {'Zhang San': 18,  'Li Si': 19, 'Wang Wu': 20}
# print(dictionary['Zhao Liu']) # KeyError: 'Zhao Liu'

# Solution 1: use if statement
print(dictionary['Zhao Liu'] if 'Zhao Liu' in dictionary else 'Dictionary does not have this person')

# Solution 2: the key specified by get() method does not exist and returns a default value
print(dictionary.get('Zhao Liu')) # None
print(dictionary.get('Zhao Liu', 'Dictionary does not have this person'))

Ergodic dictionary

# The items() method gets the 'key value pair' tuple list
dictionary = {'Zhang San': 18,  'Li Si': 19, 'Wang Wu': 20}
for item in dictionary.items():
    print(item)

"""
//Output results:
('Zhang San', 18)
('Li Si', 19)
('Wang Wu', 20)
"""

# Get each key and value
for key,value in dictionary.items():
    print(key, value)

"""
//Output results:
//Zhang San 18
//Li Si 19
//Wang Wu 20
"""

# values() returns a list of 'values' for the dictionary
print(dictionary.values())  # dict_values([18, 19, 20])
for value in dictionary.values():
    print(value)

# keys() returns the dictionary's list of 'keys'
print(dictionary.keys())    # dict_keys(['zhang San ','li Si','wang Wu '])
for key in dictionary.keys():
    print(key)

Add, modify, and delete dictionary elements

# Add to
dictionary = dict((('Zhang San', 18), ('Li Si', 20), ('Wang Wu', 33)))
dictionary['Zhao Liu'] = 29
print(dictionary)  # {'Zhang San': 18, 'Li Si': 20, 'Wang Wu': 33, 'Zhao Liu': 29}

# modify
dictionary['Li Si'] = 100
print(dictionary)   # {'Zhang San': 18, 'Li Si': 100, 'Wang Wu': 33, 'Zhao Liu': 29}


# Delete del
del dictionary['Li Si']
print(dictionary)   # {'Zhang San': 18, 'Wang Wu': 33, 'Zhao Liu': 29}

# del dictionary['haha']  # Delete the exception thrown by the nonexistent key KeyError: 'haha'
# Solve
if 'haha' in dictionary:
    del dictionary['Ha-ha']
print(dictionary)

Dictionary derivation

• Generate a dictionary quickly, similar to list derivation

# Generate a dictionary of 4 random numbers, where the key of the dictionary is represented by a number
import random

randomdict = {i:random.randint(10, 100) for i in range(1, 5)}
print('The generated dictionary is: ', randomdict)

# List generation dictionary
name = ['Zhang San', 'Li Si', 'Wang Wu']
age = [18, 19, 20]
dictionary = {i: j for i, j in zip(name, age)}
print(dictionary)```