>>> a = oct(10)

>>> a
'0o12'
>>> type(a) # 返回結果類型是字符串
<class 'str'>

>>> oct(10.0) # 浮點數不能轉換成8進制
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') # 字符串不能轉換成8進制
Traceback (most recent call last):
 File "<pyshell#4>", line 1, in <module>
  oct('10')
TypeError: 'str' object cannot be interpreted as an integer

# 未定義__index__函數，不能轉換
>>> 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

# 定義了__index__函數，但是返回值不是int類型，不能轉換
>>> 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)

# 定義了__index__函數，而且返回值是int類型，能轉換
>>> 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'