Understanding and Using Python Dictionaries: Creation, Access, Modification, Deletion, Traversal, and Nesting

1. Dictionary Understanding

Python dictionaries are mutable containers that store key‑value pairs, where each pair is separated by a colon and the whole structure is enclosed in curly braces.

2. Accessing Dictionaries

2.1 Access Keys

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
keys = my_dict.keys()
print(keys)  # 输出: dict_keys(['name', 'age', 'city'])

2.2 Access Values

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
values = my_dict.values()
print(values)  # 输出: dict_values(['Alice', 30, 'New York'])

3. Creating Dictionaries and Accessing Values

3.1 Create and Access

# 创建字典
my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
# 访问字典中的值
print(my_dict['name'])  # 输出: Alice
print(my_dict.get('age'))  # 输出: 30

3.2 Dictionary Length

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
print(len(my_dict))  # 输出: 3

3.3 Data Types

my_dict = {
    'name': 'Alice',  # 字符串
    'age': 30,        # 整数
    'is_student': False,  # 布尔值
    'grades': [95, 88, 92]  # 列表
}
print(my_dict)  # 输出: {'name': 'Alice', 'age': 30, 'is_student': False, 'grades': [95, 88, 92]}

4. Modifying Dictionaries

4.1 Single Change

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
my_dict['age'] = 31
print(my_dict)  # 输出: {'name': 'Alice', 'age': 31, 'city': 'New York'}

4.2 Multiple Changes

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
my_dict.update({'age': 31, 'city': 'Los Angeles'})
print(my_dict)  # 输出: {'name': 'Alice', 'age': 31, 'city': 'Los Angeles'}

5. Adding Dictionary Items

5.1 Direct Assignment

my_dict = {'name': 'Alice', 'age': 30}
my_dict['city'] = 'New York'
print(my_dict)  # 输出: {'name': 'Alice', 'age': 30, 'city': 'New York'}

5.2 Using update()

my_dict = {'name': 'Alice', 'age': 30}
my_dict.update({'city': 'New York', 'email': '[email protected]'})
print(my_dict)  # 输出: {'name': 'Alice', 'age': 30, 'city': 'New York', 'email': '[email protected]'}

6. Deleting Dictionary Items

6.1 Delete Specific Key

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
del my_dict['age']
print(my_dict)  # 输出: {'name': 'Alice', 'city': 'New York'}

6.2 Using pop()

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
removed_value = my_dict.pop('age')
print(removed_value)  # 输出: 30
print(my_dict)  # 输出: {'name': 'Alice', 'city': 'New York'}

6.3 Clear Dictionary

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
my_dict.clear()
print(my_dict)  # 输出: {}

7. Traversing Dictionaries

7.1 Iterate Keys

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
for key in my_dict:
    print(key)

7.2 Iterate Values

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
for value in my_dict.values():
    print(value)

7.3 Iterate Key‑Value Pairs

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
for key, value in my_dict.items():
    print(f"{key}: {value}")

8. Copying Dictionaries

8.1 Using copy() Method

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
new_dict = my_dict.copy()
print(new_dict)  # 输出: {'name': 'Alice', 'age': 30, 'city': 'New York'}

8.2 Using dict Constructor

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}
new_dict = dict(my_dict)
print(new_dict)  # 输出: {'name': 'Alice', 'age': 30, 'city': 'New York'}

9. Nested Dictionaries

9.1 Create Nested Dictionary

nested_dict = {
    'person1': {'name': 'Alice', 'age': 30},
    'person2': {'name': 'Bob', 'age': 25}
}
print(nested_dict)  # 输出: {'person1': {'name': 'Alice', 'age': 30}, 'person2': {'name': 'Bob', 'age': 25}}

9.2 Access Nested Dictionary

nested_dict = {
    'person1': {'name': 'Alice', 'age': 30},
    'person2': {'name': 'Bob', 'age': 25}
}
print(nested_dict['person1']['name'])  # 输出: Alice

9.3 Modify Nested Dictionary

nested_dict = {
    'person1': {'name': 'Alice', 'age': 30},
    'person2': {'name': 'Bob', 'age': 25}
}
nested_dict['person1']['age'] = 31
print(nested_dict)  # 输出: {'person1': {'name': 'Alice', 'age': 31}, 'person2': {'name': 'Bob', 'age': 25}}