Python 3文件对象是 io模块，针对该模块中的 ABC类进行测试:>

Python 3 file objects are part of the io module, test against ABC classes in that module:

from io import IOBase

if isinstance(someobj, IOBase):

在Python 2中不要使用type(obj) == file；您应该使用isinstance(obj, file)代替.即使那样，您仍要测试功能； io ABC允许您执行的操作； isinstance()函数将为实现抽象方法的所有方法的任何对象返回True.基类定义.

Don't use type(obj) == file in Python 2; you'd use isinstance(obj, file) instead. Even then, you would want to test for the capabilities; something the io ABCs let you do; the isinstance() function will return True for any object that implements all the methods the Abstract Base Class defines.

演示:

>>> from io import IOBase
>>> fh = open('/tmp/demo', 'w')
>>> isinstance(fh, IOBase)
True
>>> isinstance(object(), IOBase)
False