[Python3 填坑] 013 几个类相关函数的举例

目录

• 1. print( 坑的信息 )
• 2. 开始填坑
  • 2.1 issubclass()
  • 2.2 isinstance()
  • 2.3 hasattr()
  • 2.4 getattr()
  • 2.5 setattr()
  • 2.6 delattr()

---

1. print( 坑的信息 )

• 挖坑时间：2019/04/07
• 明细

坑的编码	内容
Py023-1	对 issubclass，isinstance，hasattr，getattr，setattr，delattr 举例

2. 开始填坑

2.1 issubclass()

• 官方文档

issubclass(cls, class_or_tuple, /)
    Return whether 'cls' is a derived from another class or is the same class.

• 大致意思
  • 判断 cls 是否派生自 class_or_tuple，并返回相应的值
• 举例

class A(object):
    pass

class B(A):
    pass

class C(object):
    pass

print("B 是 A 的子类吗：", issubclass(B, A))
print("C 是 A 的子类吗：", issubclass(C, A))
print("B 是 object 的子类吗：", issubclass(B, object))

>>>

B 是 A 的子类吗： True

C 是 A 的子类吗： False

B 是 object 的子类吗： True

2.2 isinstance()

• 官方文档

isinstance(obj, class_or_tuple, /)
    Return whether an object is an instance of a class or of a subclass thereof.

• 大致意思
  • 判断 obj 是否是 class_or_tuple 的实例，并返回相应的值
• 举例

class A(object):
    pass

class B(object):
    pass

a = A()
b = B()

print("a 是 A 的实例吗：", isinstance(a, A))
print("A 是 A 的实例吗：", isinstance(A, A))
print("b 是 A 的实例吗：", isinstance(b, A))

>>>

a 是 A 的实例吗： True

A 是 A 的实例吗： False

b 是 A 的实例吗： False

2.3 hasattr()

• 官方文档

hasattr(obj, name, /)
    Return whether the object has an attribute with the given name.

• 大致意思
  • 判断 obj 是否具有属性 name，并返回相应的值
• 举例

class A():
    name = "York"

a = A()

print("a 有属性 name 吗：", hasattr(a, "name" ))
print("a 有属性 age 吗：", hasattr(a, "age" ))

>>>

a 有属性 name 吗： True

a 有属性 age 吗： False

2.4 getattr()

• 官方文档

getattr(...)
    getattr(object, name[, default]) -> value

    Get a named attribute from an object;
    getattr(x, 'y') is equivalent to x.y.
    When a default argument is given, it is returned when the attribute doesn't exist;
    without it, an exception is raised in that case.

• 大致意思
  • getattr(x, 'y') 相当于 x.y
  • 若 x 有 y 属性，则返回 x 的属性 y
  • 若 x 无 y 属性，则引发异常
• 举例

class A():
    name = "York"

a = A()

print("a.name: ", getattr(a, "name" ))
print("a.age: ", getattr(a, "age" ))

>>>

a.name:  York
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-5-6ee17f32b693> in <module>()
      5
      6 print("a.name: ", getattr(a, "name" ))
----> 7 print("a.age: ", getattr(a, "age" ))

AttributeError: 'A' object has no attribute 'age'

2.5 setattr()

• 官方文档

setattr(obj, name, value, /)
    Sets the named attribute on the given object to the specified value.

    setattr(x, 'y', v) is equivalent to ``x.y = v''

• 大致意思
  • 给类属性赋值
  • setattr(x, 'y', v) 相当于 x.y = v
• 举例

class A():
    name = "York"

a = A()

print("更改前的 a.name: ", a.name)
setattr(a, "name", "Fish")
print("更改前后 a.name: ", a.name)

>>>

更改前的 a.name: York

更改前后 a.name: Fish

2.6 delattr()

• 官方文档

delattr(obj, name, /)
    Deletes the named attribute from the given object.

    delattr(x, 'y') is equivalent to ``del x.y''

• 大致意思
  • 删除类属性
  • delattr(x, 'y') 相当于 del x.y
• 举例

class A():
    name = "York"
    age = 18

a = A()

print("a.name: ", a.name)
print("a.age: ", a.age)

delattr(A, "age")

print("a.name: ", a.name)
print("a.nage ", a.age)

>>>

a.name:  York
a.age:  18
a.name:  York

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-14-1b1893332691> in <module>()
     11
     12 print("a.name: ", a.name)
---> 13 print("a.nage ", a.age)

AttributeError: 'A' object has no attribute 'age'