Pillow/PIL/_util.py

import os

if bytes is str:
    def isStringType(t):
        return isinstance(t, basestring)
    def isPath(f):
        return isinstance(f, basestring)
else:
    def isStringType(t):
        return isinstance(t, str)
    def isPath(f):
        return isinstance(f, (bytes, str))

# Checks if an object is a string, and that it points to a directory.
def isDirectory(f):
    return isPath(f) and os.path.isdir(f)