如何在Python中创建字典

如何在Python中创建字典

在Python中，字典是一种无序的数据项序列，可用于记录数据项，就像地图一样。与仅包含一个对象作为对象的备选数据结构不同，字典包含一个键值对。字典包括一个键-值字段，以提高此数据类型的效率。

创建字典

我们可以通过将一组对象放在大括号中并用逗号分隔它们来在Python中创建字典。字典跟踪一对条目，其中一部分称为键，另一部分称为键的值，被称为键-值对。我们可以将任何数据类型作为键的值存储，并给两个键赋予相同的值，但键应是不可变且唯一的。

代码

# Initializing a dictionary with some elements 
Dictionary = {1: 'Javatpoint', 2: 'Python', 3: 'Dictionary'}
print("\nDictionary created using curly braces: ")
print(Dictionary)
# Creating a Dictionary with keys of different data types
Dictionary = {'Website': 'Javatpoint', 3: [2, 3, 5, 'Dictionary']}
print("\nDictionary with keys of multiple data type: ")
print(Dictionary)

输出：

Dictionary created using curly braces: 
{1: 'Javatpoint', 2: 'Python', 3: 'Dictionary'}

Dictionary with keys of multiple data type: 
{'Website': 'Javatpoint', 3: [2, 3, 5, 'Dictionary']}

内置方法dict()也可以用于生成字典。只需放置两个花括号{}，就可以创建一个空字典。

代码

# Initializing an empty Dictionary
Dictionary = {}
print("An empty Dictionary: ")
print(Dictionary)

# Creating a Dictionary using in-built dict() method
Dictionary = dict({1: 'Python', 2: 'Javatpoint', 3:'Dictionary'})
print("\nDictionary created by using dict() method: ")
print(Dictionary)

# Creating dictionary by key:value pair format
Dictionary = dict([(1, 'Javatpoint'), (2, 'Python'), (3, 'Dictionary')])
print("\nDictionary with key:value pair format: ")
print(Dictionary)

输出：

An empty Dictionary: 
{}

Dictionary created by using dict() method: 
{1: 'Python', 2: 'Javatpoint', 3: 'Dictionary'}

Dictionary with key:value pair format: 
{1: 'Javatpoint', 2: 'Python', 3: 'Dictionary'}

添加元素到字典中

Python字典中的元素可以通过不同的方法来插入。可以使用特定格式Dictionary[Key] = ‘Value’将项目添加到字典中。我们可以使用内置的update()函数来更新字典中的当前键。嵌套的键：值也可以插入到现有字典中。如果字典中存在键值组合，则修改该键的值；如果不存在，则创建一个新键并将其添加到具有给定值的字典中。

代码

# Initializing an empty Dictionary
Dictionary = {}
print("The empty Dictionary: ")
print(Dictionary)

# Inserting key:value pairs one at a time
Dictionary[0] = 'Javatpoint'
Dictionary[2] = 'Python'
Dictionary.update({ 3 : 'Dictionary'})
print("\nDictionary after addition of these elements: ")
print(Dictionary)

# Adding a list of values to a single key
Dictionary['list_values'] = 3, 4, 6
print("\nDictionary after addition of the list: ")
print(Dictionary)

# Updating values of an already existing Key
Dictionary[2] = 'Tutorial'
print("\nUpdated dictionary: ")
print(Dict)

# Adding a nested Key to our dictionary
Dictionary[5] = {'Nested_key' :{1 : 'Nested', 2 : 'Key'}}
print("\nAfter addtion of a Nested Key: ")
print(Dictionary)

输出：

The empty Dictionary: 
{}

Dictionary after addition of these elements: 
{0: 'Javatpoint', 2: 'Python', 3: 'Dictionary'}

Dictionary after addition of the list: 
{0: 'Javatpoint', 2: 'Python', 3: 'Dictionary', 'list_values': (3, 4, 6)}

Updated dictionary: 
{1: 'Javatpoint', 2: 'Python'}

After addtion of a Nested Key: 
{0: 'Javatpoint', 2: 'Tutorial', 3: 'Dictionary', 'list_values': (3, 4, 6), 5: {'Nested_key': {1: 'Nested', 2: 'Key'}}}

删除字典中的元素

使用pop()函数可以从字典中删除特定的项目。该函数返回被删除的键的值。

popitem()函数从给定的字典中删除并返回任意的(key, value)元素对。我们可以使用clear()函数一次性删除所有对象。

我们还可以使用del关键字删除单个项目或整个字典。

代码

# Program to show how to remove elements from a dictionary

# initializing a dictionary
Dictionary = {1: 'a', 2: 'b', 3: 'c', 4: 'd', 5: 'e'}

# removing a key:value pair from the dictionary using pop()
Dictionary.pop(4)
print("\nAfter removing a key using pop(): ")
print(Dictionary)

# remove any item at random using popitem()
Dictionary.popitem()
print("\nAfter removing an arbitrary key: ")
print(Dictionary)

# remove all the items present in dictionary
print("\nAfter removing all the items: ")
Dictionary.clear()
print(Dictionary)

# deleting the dictionary variable
del Dictionary

# Printing dictionary after deleting it
try:
    print(Dictionary)
except:
    print('No dictionary of the given name')

输出:

After removing a key using pop(): 
{1: 'a', 2: 'b', 3: 'c', 5: 'e'}

After removing an arbitrary key: 
{1: 'a', 2: 'b', 3: 'c'}

After removing all the items: 
{}
No dictionary of the given name

Python 字典方法

我们可以使用的字典技巧如下所示。其中一些已在本教程中提到过。