Because file can't use in python 3.
In python 2, we judge a file type can do this:
with open("xxx.txt") as f:
if isinstance(f, file):
print("ok!")
In python 3, we can do this:
import io
with open("xxx.txt") as f:
if isinstance(f, io.IOBase)
print("ok!")
But the second code can't work in python 2.
So, is there a way to judge a file type both work in python 2 and python 3.
You can test for both with a tuple; use a NameError guard to make this work on Python 3:
import io
try:
filetypes = (io.IOBase, file)
except NameError:
filetypes = io.IOBase
isinstance(f, filetypes)
You need to test for both on Python 2 as you can use the io library there too.
However, it is better to use duck typing rather that testing for io.IOBase; see Check if object is file-like in Python for motivations. Better to check if the method you need is present:
if hasattr(f, 'read'):
Note that io.IOBase doesn't even include read. And in Python 2, StringIO.StringIO is a file-like object too, one that isinstance(.., file) will not support.
