undefined-variable Warning for python 3.x in pylint

Question

I am writing a python script but I just faced this issue regarding pylint checks in python 3.x :

class m(object):
    def check_infile(self):
        infile = None
        if not isinstance(infile, file):
            print("infile variable is not a file type.")

Output:

E: 56,38: Undefined variable 'file' (undefined-variable)

I tried to eliminate this issue by adding # pylint: disable=E0602, undefined-variable, E0603 but nothing helps. any suggestion?

Answer 1

In python3.x, file isn't a valid type:

Python 3.5.1 (v3.5.1:37a07cee5969, Dec  5 2015, 21:12:44) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> file
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'file' is not defined

So pylint is right here and you probably don't want to silence it. You might want to check if the object has file-like methods:

if not getattr(infile, 'read', None):
    print('definitely not a file...')