如何在Python中获取类属性列表？

类是用户定义的蓝图或原型，从中创建对象。类提供了一种将数据和功能捆绑在一起的方法。创建一个新类会创建一种新类型的对象，允许创建该类型的新实例。每个类实例都可以附加属性以维护其状态。类实例也可以具有用于修改其状态的方法（由其类定义）。

例子：

# Python program to demonstrate
# classes
  
  
class Student:
      
    # class variable
    stream = "COE"
      
    # Constructor
    def __init__(self, name, roll_no):
          
        self.name = name
        self.roll_no = roll_no
          
# Driver's code
a = Student("Shivam", 3425)
b = Student("Sachin", 3624)
  
print(a.stream)
print(b.stream)
print(a.name)
print(b.name)
  
# Class variables can be accessed
# using class name also 
print(Student.stream) 

输出 ：

COE
COE
Shivam
Sachin
COE

注意：有关详细信息，请参阅Python类和对象。

获取类属性列表

了解我们正在使用的属性很重要。对于小数据，很容易记住属性的名称，但在处理大数据时，很难记住所有属性。幸运的是，我们有一些Python函数可用于此任务。

方法 1：为了获取一个类的所有属性、方法以及一些继承的魔法方法的列表，我们使用了一个名为dir()的内置函数。

例子：

class Number :
      
    # Class Attributes
    one = 'first'
    two = 'second'
    three = 'third'
      
    def __init__(self, attr):
        self.attr = attr
          
    def show(self): 
        print(self.one, self.two, self.three, self.attr)
          
n = Number(2)
n.show()
  
  
  
# Passing both the object 
# and class as  argument
# to the dir method
print('\nBy passing object of class')
print(dir(n))
  
print('\nBy passing class itself ')
print(dir(Number))

输出 ：

first second third 2

By passing object of class
[‘__class__’, ‘__delattr__’, ‘__dict__’, ‘__dir__’, ‘__doc__’, ‘__eq__’, ‘__format__’, ‘__ge__’, ‘__getattribute__’, ‘__gt__’, ‘__hash__’, ‘__init__’, ‘__init_subclass__’, ‘__le__’, ‘__lt__’, ‘__module__’, ‘__ne__’, ‘__new__’, ‘__reduce__’, ‘__reduce_ex__’, ‘__repr__’, ‘__setattr__’, ‘__sizeof__’, ‘__str__’, ‘__subclasshook__’, ‘__weakref__’, ‘attr’, ‘one’, ‘show’, ‘three’, ‘two’]

By passing class itself
[‘__class__’, ‘__delattr__’, ‘__dict__’, ‘__dir__’, ‘__doc__’, ‘__eq__’, ‘__format__’, ‘__ge__’, ‘__getattribute__’, ‘__gt__’, ‘__hash__’, ‘__init__’, ‘__init_subclass__’, ‘__le__’, ‘__lt__’, ‘__module__’, ‘__ne__’, ‘__new__’, ‘__reduce__’, ‘__reduce_ex__’, ‘__repr__’, ‘__setattr__’, ‘__sizeof__’, ‘__str__’, ‘__subclasshook__’, ‘__weakref__’, ‘one’, ‘show’, ‘three’, ‘two’]

方法 2：另一种查找属性列表的方法是使用模块inspect 。这个模块提供了一个名为getmemebers()的方法，它返回一个类属性和方法的列表。

示例 1：

import inspect
  
  
class Number :
      
    # Class Attributes
    one = 'first'
    two = 'second'
    three = 'third'
      
    def __init__(self, attr):
        self.attr = attr
          
    def show(self): 
        print(self.one, self.two, self.three, self.attr)
          
          
# Driver's code
n = Number(2)
n.show()
  
# getmembers() returns all the 
# members of an object 
for i in inspect.getmembers(n):
      
    # to remove private and protected
    # functions
    if not i[0].startswith('_'):
          
        # To remove other methods that
        # doesnot start with a underscore
        if not inspect.ismethod(i[1]): 
            print(i)

输出 ：

first second third 2
('attr', 2)
('one', 'first')
('three', 'third')
('two', 'second')

方法 3：要查找属性，我们还可以使用魔术方法__dict__ 。此方法仅返回实例属性。

例子：

class Number :
      
    # Class Attributes
    one = 'first'
    two = 'second'
    three = 'third'
      
    def __init__(self, attr):
        self.attr = attr
          
    def show(self): 
        print(self.one, self.two, self.three, self.attr)
          
# Driver's code
n = Number(2)
n.show()
  
# using __dict__ to access attributes
# of the object n along with their values
print(n.__dict__)
  
# to only access attributes
print(n.__dict__.keys())
  
# to only access values
print(n.__dict__.values())

输出：

first second third 2
{'attr': 2}
dict_keys(['attr'])
dict_values([2])