Python教程-Python del 语句

介绍

在Python中，del关键字通常用于删除一个对象。由于Python中的一切都表示某种对象，因此del关键字也可用于删除列表、变量、列表的部分等。del语句不返回任何类型的值。

del 语句的语法

del obj_name  

注意：del是一个关键字，obj_name可以是列表、字典、用户定义的对象、变量等。

del 语句的示例

让我们看一些del语句的示例并尝试删除一些项目。

示例 1：在此程序中，我们将使用del语句删除一个变量

a = 13  
b = 5  
c = a + b + 13 - 1 + 5  
print(c)  
  
# delete the c variables  
del c  
  
# print c variable after delete  
print(c)  

输出:

35

Traceback (most recent call last):
  File "", line 10, in 
NameError: name 'c' is not defined
>

示例 2：在此程序中，我们将使用del关键字删除列表和切片列表

items_1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]  
items_2 =["a", "b", "c", "d", "e", "f"]  
  
# print the items_1 and items_2  
print(items_1)  
print(items_2)  
  
# delete the 3rd element of items_1  
del items_1[2]  
  
# check if the 3rd element in items_1 is deleted or not  
print(items_1)  
  
# slice items_1 from index 4 to 9  
del items_1[4:9]  
  
# check if the elements from index 4 to 9 in items_1 is deleted or not  
print(items_1)  
  
# delete the 2nd element of items_2  
del items_2[1]  
  
# check if the 2nd element in items_2 is deleted or not  
print(items_2)  
  
# delete items_2  
del items_2  
  
# check if items_2 exists  
print(items_2)  

输出:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
['a', 'b', 'c', 'd', 'e', 'f']
[0, 1, 3, 4, 5, 6, 7, 8, 9]
[0, 1, 3, 4]
['a', 'c', 'd', 'e', 'f']

Traceback (most recent call last):
  File "", line 30, in 
NameError: name 'items_2' is not defined
>

示例 3：在此程序中，我们将使用del语句删除字典和键值对

dictionary_1 = {"up": "down", "forward": "backward", "small": "down"}  
dictionary_2 = {"short": "long", "you": "me", "Jack": "John"}  
  
# check if dictionary_1 and dictionary_2 exists  
print(dictionary_1)  
print(dictionary_2)  
  
# delete key-value pair with key "up" from dictionary_1  
del dictionary_1["up"]  
  
# check if the key-value pair with key "up" from dictionary_1 is deleted  
print(dictionary_1)  
  
# delete dictionary_2  
del dictionary_2  
  
# check if dictionary_2 exists  
print(dictionary_2)  

输出:

{'up': 'down', 'forward': 'backward', 'small': 'down'}
{'short': 'long', 'you': 'me', 'Jack': 'John'}
{'forward': 'backward', 'small': 'down'}

Traceback (most recent call last):
   File "", line 18, in 
NameError: name 'dictionary_2' is not defined
>

示例 4：删除用户定义的对象

# defining a class  
class employee:  
    name = "John wik"  
    age = 26  
    address = "C-26, London"  
    phone_no = 61562347    
  
# declaring the object to the employee class  
emp = employee()  
  
# print the employee data  
print("Name: ", emp.name)  
print("Age: ", emp.age)  
print("Address: ", emp.address)  
print("Phone No: ", emp.phone_no)  
  
# deleting the object   
del emp  
  
# printing values - will generate NameError  
print("Name: ", emp.name)  
print("Age: ", emp.age)  
print("Address: ", emp.address)  
print("Phone No: ", emp.phone_no)  

输出:

Name:  John wik
Age:  26
Address:  C-26, London
Phone No:  61562347
Traceback (most recent call last):
   File "", line 21, in 
NameError: name 'emp' is not defined
>