Python| getattr() 方法

Python getattr()函数用于访问对象的属性值，并且还提供了在密钥不可用的情况下执行默认值的选项。

Syntax : getattr(obj, key, def)

Parameters : 

• obj : The object whose attributes need to be processed.
• key : The attribute of object
• def : The default value that need to be printed in case attribute is not found.

Returns : Object value if value is available, default value in case attribute is not present 
and returns AttributeError in case attribute is not present and default value is not 
specified. 

getattr() 如何在Python中工作

示例 1：演示 getattr() 的工作原理

Python3

# Python code to demonstrate
# working of getattr()
 
# declaring class
class GfG:
    name = "GeeksforGeeks"
    age = 24
 
# initializing object and
# python getattr() function call
obj = GfG()
 
# use of getattr
print("The name is " + getattr(obj, 'name'))
 
# use of getattr with default
print("Description is " + getattr(obj,
                                  'description',
                                  'CS Portal'))
 
# use of getattr without default
print("Motto is " + getattr(obj, 'motto'))

输出：

The name is GeeksforGeeks
Description is CS Portal

例外：

AttributeError: GfG instance has no attribute 'motto'

示例 2：未找到命名属性时的 getattr()

Python3

# Python code to demonstrate
# working of getattr()
 
# declaring class
class GfG:
    name = "GeeksforGeeks"
    age = 24
 
 
# initializing object
obj = GfG()
 
# use of getattr without default
print("Gender is " + getattr(obj, 'gender'))

输出：

AttributeError: 'GfG' object has no attribute 'gender'

示例 3：性能分析和 getattr Python带参数

Python3

# Python code to demonstrate
# performance analysis of getattr()
import time
 
# declaring class
class GfG:
    name = "GeeksforGeeks"
    age = 24
 
# initializing object
obj = GfG()
 
# use of getattr to print name
start_getattr = time.time()
print("The name is " + getattr(obj, 'name'))
print("Time to execute getattr " + str(time.time() - start_getattr))
 
# use of conventional method to print name
start_obj = time.time()
print("The name is " + obj.name)
print("Time to execute conventional method " + str(time.time() - start_obj))

输出：

The name is GeeksforGeeks
Time to execute getattr 5.0067901611328125e-06
The name is GeeksforGeeks
Time to execute conventional method 1.1920928955078125e-06

示例 4：getattr Python默认值

Python3

# Python code to demonstrate
# working of getattr()
 
# declaring class
class GfG:
    name = "GeeksforGeeks"
    age = 24
 
# initializing object
obj = GfG()
 
# use of getattr without default
print("Motto is " + getattr(obj, 'motto'))

输出：

AttributeError: 'GfG' object has no attribute 'motto'

示例 5： Python getattr()函数调用

Python3

# Python code to demonstrate
# working of getattr()
 
# declaring class
class GfG:
     
    def __init__(self, name, age):
        self.name = name
        self.age = age
 
    def call(self, x):
        print(f"{self.name} called with parameters '{x}'")
        return
 
# initializing object
obj = GfG("Vivek", 10)
print(obj)
print(GfG)
print(getattr(obj,'call'))
 
getattr(obj,'call')('arg')

输出：

<__main__.GfG object at 0x0000023C1ED92748>

>
Vivek called with parameters 'arg'

结果：传统方法比 getattr() 花费的时间更少，但是当必须使用默认值以防缺少属性时，getattr() 是一个不错的选择。

应用： getattr() 有很多应用，其中一些已经在缺少对象属性的情况下被提及，在一些表单属性是可选的 Web 开发中。在机器学习特征集合的情况下也很有用，以防某些特征有时在数据集合中丢失。