当前位置：首页 > news >正文

Python-字典，从基础到进阶用法大总结，进来查漏补缺

news 来源：原创 2024/5/14 11:06:59

在这里插入图片描述
B站|公众号：啥都会一点的研究生

hello，我是啥都生，本期将Python中字典涉及的从基础到进阶用法，全部总结归纳，一起看看吧

计算机中的标准数据结构通常称为“映射”。在Python中，这种结构称为“字典”。当有键/值对数据（一个映射到输出的输入）时，使用字典是最方便的

假设有如下数据

name = "CaiXK"
age = 38
height = 163.1415926
hobby = ["rap", "basketball", "python"]
location = (34.228, 26.093)

以name = "CaiXK"为例，构成完整键值对，name为键，"CaiXK"为值。有两种构建列表的方式将上述数据进行存储，第一种，直接使用大括号，键与值间用冒号配对，键值对间用逗号隔开

dict1 = {"name" : "CaiXK", "age" : 38, "height" : 163.1415926, "hobby" : ["rap", "basketball", "python"], "location" : (34.228, 26.093)}

print(dict1)

>>> {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python'], 'location': (34.228, 26.093)}

第二种，使用内置方法dict()，注意与第一种方法的区别，键值用等号连接，键值对依然用逗号隔开

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

print(dict1)

>>> {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python'], 'location': (34.228, 26.093)}

此外，使用fromkeys() 函数用于创建新字典，以序列中的元素做字典的键，所有键对应的初始值默认为None，可自定义初始值

keys = ('name', 'age', 'sex')

dict1 = dict.fromkeys(keys)
dict2 = dict.fromkeys(keys, 1)

print(dict1)
print(dict2)

>>> {'name': None, 'age': None, 'sex': None}
>>> {'name': 1, 'age': 1, 'sex': 1}

需特别注意的是，键不允许重复，若使用dict方式创建字典并多次给同一个键赋值，则会触发报错

dict1 = dict(name = "ZhangS", name = "LiS", name = "CaiXK")

print(dict1["name"])

>>> File "script.py", line 5
    dict1 = dict(name = "ZhangS", name = "LiS", name = "CaiXK")
                                  ^
SyntaxError: keyword argument repeated

Exited with error status 1

而使用大括号方式创建，则只保留最后一次写入的键值对数据

dict1 = {"name" : "ZhangS", "name" : "LiS", "name" : "CaiXK"}

print(dict1["name"])

>>> CaiXK

此外，必须保证键是不可变，也就是仅支持数字、字符串、元组

dict1 = {1 : 2, (22, 33) : "44", "55" : 66}

print(dict1)

>>> {1: 2, (22, 33): '44', '55': 66}

字典创建完成后，可以看做N个输入对应N个输出，输入为键，输出为值，且不限定输出类型。字典的取值通过键完成索引，如下所示，注意使用中括号且引号别落下

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

name = dict1["name"]

hobby_1 = dict1["hobby"][0]

print(name, " is good at ", hobby_1)

>>> CaiXK  is good at  rap

如果试图访问取出不存在的键，则会抛出如下错误

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

Girlfriend = dict1["girlfriend"]

print(Girlfriend)

>>> Traceback (most recent call last):
  File "script.py", line 3, in <module>
    Girlfriend = dict1["girlfriend"]
KeyError: 'girlfriend'

Exited with error status 1

而使用get获取键值，若键不存在，默认返回None，也支持自定义返回数据避免错误

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

Girlfriend = dict1.get("girlfriend")

print(Girlfriend)

Girlfriend = dict1.get("girlfriend", "Peter")

print(Girlfriend)

>>> None
>>> Peter

和get()类似，若键不存在于字典中，使用setdefault自定义值，默认为None，但不同的是，会将该键值对添加至字典中

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

Girlfriend = dict1.setdefault("girlfriend", "Peter")

print(Girlfriend)
print(dict1)

>>> Peter
>>> {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python'], 'location': (34.228, 26.093), 'girlfriend': 'Peter'}

因为字典是可变对象，支持修改，可以通过如下方式完成键值对的添加

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

dict1["girlfriend"] = "ZhangH" # Han

print(dict1)

>>> {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python'], 'location': (34.228, 26.093), 'girlfriend': 'ZhangH'}

通过索引键并重新赋值完成修改

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

dict1["girlfriend"] = "LiYF" # ?

print(dict1)

>>> {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python'], 'location': (34.228, 26.093), 'girlfriend': 'LiYF'}

使用del删除指定键值对

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

del dict1["location"]

print(dict1)

>>> {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python']}

也可以删除整个字典

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

del dict1

print(dict1)

>>> Traceback (most recent call last):
  File "script.py", line 11, in <module>
    print(dict1)
NameError: name 'dict1' is not defined

Exited with error status 1

使用pop删除指定键值对并返回值

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

location = dict1.pop("location")

print(location, dict1)

>>> (34.228, 26.093) {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python']}

使用popitem随机返回并删除字典中的最后一对键和值

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

data = dict1.popitem()

print(data, dict1)

>>> ('location', (34.228, 26.093)) {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python']}

使用clear清空字典中的全部内容，注意与del不同，该对象仍存在

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

dict1.clear()

print(dict1)

>>> {}

使用copy完成字典的浅拷贝，避免因其可变带来的原始数据改动

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

dict2 = dict1
dict3 = dict1.copy()

dict1.popitem()

print(dict2)
print(dict3)

>>> {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python']}
>>> {'name': 'CaiXK', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python'], 'location': (34.228, 26.093)}

判断键是否存在于字典中使用in

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

if name in dict1:
    print(True)

>>> True

使用update将另一个字典中的键值对更新到本字典中，若键重复，则以另一字典为默认

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))
dict2 = dict(name = "WuYF", sex = "Female")

dict1.update(dict2)

print(dict1)

>>> {'name': 'WuYF', 'age': 38, 'height': 163.1415926, 'hobby': ['rap', 'basketball', 'python'], 'location': (34.228, 26.093), 'sex': 'Female'}

然后说说列表的遍历，第一种，使用items遍历每一个键值对

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

for item in dict1.items():
    print(item)

>>> ('name', 'CaiXK')
('age', 38)
('height', 163.1415926)
('hobby', ['rap', 'basketball', 'python'])
('location', (34.228, 26.093))

第二种，使用keys遍历字典中每个键，或者默认不使用内置方法

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

for key in dict1.keys(): # for key in dict1()
    print(key)

>>> name
age
height
hobby
location

第三种，使用values遍历字典中每个值

dict1 = dict(name = "CaiXK", age = 38, height = 163.1415926, hobby = ["rap", "basketball", "python"], location = (34.228, 26.093))

for value in dict1.values():
    print(value)

>>> CaiXK
38
163.1415926
['rap', 'basketball', 'python']
(34.228, 26.093)