如何检查对象是否是带有isinstance（）的文件？

Question

如何检查对象是否为文件？

>>> f = open("locus.txt", "r")
>>> type(f)
<class '_io.TextIOWrapper'>
>>> isinstance(f, TextIOWrapper)
Traceback (most recent call last):
  File "<pyshell#7>", line 1, in <module>
    isinstance(f, TextIOWrapper)
NameError: name 'TextIOWrapper' is not defined
>>> isinstance(f, _io.TextIOWrapper)
Traceback (most recent call last):
  File "<pyshell#8>", line 1, in <module>
    isinstance(f, _io.TextIOWrapper)
NameError: name '_io' is not defined
>>> isinstance(f, _io)
Traceback (most recent call last):
  File "<pyshell#9>", line 1, in <module>
    isinstance(f, _io)
NameError: name '_io' is not defined
>>> 

我的变量f是一个文本文件。当我打印出f类型的Python3解释器显示＆＃39; _io.TextIOWrapper＆＃39;时，如果我用isinstance()检查它，则抛出异常：NameError。

Answer 1

_io是io module的C实现。导入模块后，使用io.IOBase作为直接子类：

>>> import io
>>> f = open("tests.py", "r")
>>> isinstance(f, io.IOBase)
True