How to verify that a variable is of 'file' type

Question

It used to be in Python (2.6) that one could ask:

isinstance(f, file)

but now "file" is undefined (using Python 3.0)

What is the proper method for checking to see if a variable is a file now? The What'sNew docs didn't mention this...

Answer 1

def read_a_file(f)
    try:
        contents = f.read()
    except AttributeError:
        # f is not a file

substitute whatever methods you plan to use for read. This is optimal if you expect that you will get passed a file like object more than 98% of the time. If you expect that you will be passed a non file like object more often than 2% of the time, then the correct thing to do is:

def read_a_file(f):
    if hasattr(f, 'read'):
        contents = f.read()
    else:
        # f is not a file

This is exactly what you would do if you did have access to a file class to test against. (and FWIW, I too have file on 2.6) Note that this code works in 3.x as well.

Answer 2

Works for me on python 2.6... Are you in a strange environment where builtins aren't imported by default, or where somebody has done del file, or something?

Answer 3

I just checked this out on my Python 2.6:

>>> f = open('filepath', 'r'):
>>> type(f) == file
True

Hope that solves your problem