Python中的装饰器用法详细指南

在Python中, 函数是第一类对象, 这意味着–

• 功能是对象；它们可以被引用, 传递给变量并从其他函数返回。
• 函数可以在另一个函数中定义, 也可以作为参数传递给另一个函数。

装饰工是Python中非常强大且有用的工具, 因为它允许程序员修改函数或类的行为。装饰器允许我们包装另一个函数, 以扩展包装函数的行为, 而无需对其进行永久性修改。

在Decorators中, 将函数作为另一个函数的参数, 然后在包装函数内部调用。

装饰器的语法：

@gfg_decorator
def hello_decorator():
     print ( "Gfg" )
  
'''Above code is equivalent to -
  
def hello_decorator():
     print("Gfg")
      
hello_decorator = gfg_decorator(hello_decorator)'''

在上面的代码中, gfg_decorator是一个可调用的函数, 将在另一个可调用函数的顶部添加一些代码, hello_decorator函数并返回包装函数。

装饰者可以修改行为：

# defining a decorator
def hello_decorator(func):
  
     # inner1 is a Wrapper function in 
     # which the argument is called
      
     # inner function can access the outer local
     # functions like in this case "func"
     def inner1():
         print ( "Hello, this is before function execution" )
  
         # calling the actual function now
         # inside the wrapper function.
         func()
  
         print ( "This is after function execution" )
          
     return inner1
  
  
# defining a function, to be called inside wrapper
def function_to_be_used():
     print ( "This is inside the function !!" )
  
  
# passing 'function_to_be_used' inside the
# decorator to control its behavior
function_to_be_used = hello_decorator(function_to_be_used)
  
  
# calling the function
function_to_be_used()

输出如下：

Hello, this is before function execution
This is inside the function !!
This is after function execution

让我们看看上面的代码在调用" function_to_be_used"时如何逐步运行。

让我们跳到另一个例子, 我们可以轻松地使用装饰器找出函数的执行时间

# importing libraries
import time
import math
  
# decorator to calculate duration
# taken by any function.
def calculate_time(func):
      
     # added arguments inside the inner1, # if function takes any arguments, # can be added like this.
     def inner1( * args, * * kwargs):
  
         # storing time before function execution
         begin = time.time()
          
         func( * args, * * kwargs)
  
         # storing time after function execution
         end = time.time()
         print ( "Total time taken in : " , func.__name__, end - begin)
  
     return inner1
  
  
  
# this can be added to any function present, # in this case to calculate a factorial
@calculate_time
def factorial(num):
  
     # sleep 2 seconds because it takes very less time
     # so that you can see the actual difference
     time.sleep( 2 )
     print (math.factorial(num))
  
# calling the function.
factorial( 10 )

输出如下：

3628800
Total time taken in :  factorial 2.0061802864074707

如果一个函数返回一些东西怎么办–

在以上所有示例中, 这些函数均未返回任何内容, 因此没有任何问题, 但是可能需要返回的值。

def hello_decorator(func):
     def inner1( * args, * * kwargs):
          
         print ( "before Execution" )
          
         # getting the returned value
         returned_value = func( * args, * * kwargs)
         print ( "after Execution" )
          
         # returning the value to the original frame
         return returned_value
          
     return inner1
  
  
# adding decorator to the function
@hello_decorator
def sum_two_numbers(a, b):
     print ( "Inside the function" )
     return a + b
  
a, b = 1 , 2
  
# getting the value through return of the function
print ( "Sum =" , sum_two_numbers(a, b))

输出如下：

before Execution
Inside the function
after Execution
Sum = 3

首先, 你的面试准备可通过以下方式增强你的数据结构概念：Python DS课程。

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