Python内置函数(46)——oct

英文文档：

oct(x)

Convert an integer number to an octal string. The result is a valid Python expression. If x is not a Python int object, it has to define an __index__() method that returns an integer.

说明：

　　1. 函数功能将一个整数转换成8进制字符串。如果传入浮点数或者字符串均会报错。

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

　　2. 如果传入参数不是整数，则其必须是一个定义了__index__并返回整数函数的类的实例对象。

# 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'