How to check if variable is string with python 2 and 3 compatibility

Question

I\'m aware that I can use: isinstance(x, str) in python-3.x but I need to check if something is a string in python-2.x as well. Will isinstance(x, str)

Answer 1

The future library adds (to Python 2) compatible names, so you can continue writing Python 3. You can simple do the following:

from builtins import str
isinstance(x, str) 

---

To install it, just execute pip install future.

As a caveat, it only support python>=2.6,>=3.3, but it is more modern than six, which is only recommended if using python 2.5

Answer 2

Be careful! In python 2, str and bytes are essentially the same. This can cause a bug if you are trying to distinguish between the two.

>>> size = 5    
>>> byte_arr = bytes(size)
>>> isinstance(byte_arr, bytes)
True
>>> isinstance(byte_arr, str)
True

Answer 3

Maybe use a workaround like

def isstr(s):
    try:
        return isinstance(s, basestring)
    except NameError:
        return isinstance(s, str)

Answer 4

This is @Lev Levitsky's answer, re-written a bit.

try:
    isinstance("", basestring)
    def isstr(s):
        return isinstance(s, basestring)
except NameError:
    def isstr(s):
        return isinstance(s, str)

The try/except test is done once, and then defines a function that always works and is as fast as possible.

EDIT: Actually, we don't even need to call isinstance(); we just need to evaluate basestring and see if we get a NameError:

try:
    basestring  # attempt to evaluate basestring
    def isstr(s):
        return isinstance(s, basestring)
except NameError:
    def isstr(s):
        return isinstance(s, str)

I think it is easier to follow with the call to isinstance(), though.

Answer 5

What about this, works in all cases?

isinstance(x, ("".__class__, u"".__class__))

Answer 6

type(string) == str

returns true if its a string, and false if not