Python | getattr()方法
Python getattr() 函数用于访问对象的属性值，还提供了一个在密钥不可用时执行默认值的选项。
语法: getattr(obj，key，def)
参数:
- obj : 需要处理属性的对象。
- 键:对象的属性
- def : 找不到属性需要打印的默认值。
如果值可用，则返回:对象值，如果属性不存在，则返回默认值 ，如果属性不存在，且未指定默认值 ，则返回属性错误。
getattr()在 Python 中的工作原理
示例 1: 演示 getattr()的工作
Python 3
# 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: 找不到命名属性时的 getattr()
Python 3
# 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:性能分析和带参数的 getattr python
Python 3
# 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
Python 3
# 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
Python 3
# 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>
<class '__main__.GfG'>
<bound method GfG.call of <__main__.GfG object at 0x0000023C1ED92748>>
Vivek called with parameters 'arg'
结果:常规方法比 getattr()花费的时间少，但是当在缺少属性的情况下必须使用默认值时，getattr()是一个不错的选择。
应用程序:getattr()有许多应用程序，其中一些已经在缺少对象属性的情况下提到过，在 web 开发中，一些表单属性是可选的。在机器学习特征收集的情况下也很有用，以防某些特征有时在数据收集中丢失。
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