> a = oct(10)

> a
'0o12'
> type(a) # 返回结果类型是字符串
<class 'str'>

> oct(10.0) # 浮点数不能转换成8进制
Traceback (most recent call last):
 File "<pyshell#3>", line 1, in <module>
  oct(10.0)
TypeError: 'float' object cannot be interpreted as an integer

> oct('10') # 字符串不能转换成8进制
Traceback (most recent call last):
 File "<pyshell#4>", line 1, in <module>
  oct('10')
TypeError: 'str' object cannot be interpreted as an integer

# 未定义__index__函数，不能转换
> class Student:
  def __init__(self,name,age):
    self.name = name
    self.age = age
  
> a = Student('Kim',10)
> oct(a)
Traceback (most recent call last):
 File "<pyshell#12>", line 1, in <module>
  oct(a)
TypeError: 'Student' object cannot be interpreted as an integer

# 定义了__index__函数，但是返回值不是int类型，不能转换
> class Student:
  def __init__(self,name,age):
    self.name = name
    self.age = age
  def __index__(self):
    return self.name

> a = Student('Kim',10)
> oct(a)
Traceback (most recent call last):
 File "<pyshell#18>", line 1, in <module>
  oct(a)
TypeError: __index__ returned non-int (type str)

# 定义了__index__函数，而且返回值是int类型，能转换
> class Student:
  def __init__(self,name,age):
    self.name = name
    self.age = age
  def __index__(self):
    return self.age

> a = Student('Kim',10)
> oct(a)
'0o12'