Untitled

What is the most preferred way to pass object attributes to a function in Python?
class my_file_obj:
    def __init__(self,filename):
        self.filename = filename
        self.owner = None
        self.file_type = None
        self.fileflag = 0
        self.md5 = None

some_function(file_obj1)

# with this call the file_obj1 object reference is sent to some_function()
some_function(file_obj1)

# with this call there is no pass by reference. If filename is a
# string it is copied to some_function
some_function(file_obj1.filename)

# same as before, but here you are allocating a new var and copying the content
# to some_function
the_filename = file_obj1.filename
some_function(the_filename)

def some_function(file_thingy):
   with open(file_thingy.filename, 'w') as f:
       f.write("Icky Icky Icky Patang NeeeeWom!")

def do_duck_things(a_duck):
    print(a_duck.appearance)
    a_duck.waddle()
    a_duck.quack()
    print("It must be a duck!")

class Duck:
    def __init__(self):
        self.appearance = "White, like the AFLAC duck"

    def quack(self):
        print("Quaaaaaack!")

    def waddle(self):
        print("The duck waddles.")

class UglyDuckling:
    def __init__(self):
        self.appearance = "Suspiciously like a baby goose"

    def waddle(self):
        print("The ugly duckling waddles a bit like a duck.")

    def quack(self):
        print("Hoooonk!")

class Human:
    def __init__(self):
        self.appearance = "Looks like a human in a duck costume"

    def waddle(self):
        print("Surprisingly, he waddles quite like a duck.")

    def quack(self):
        print("<A sound quite like Donald Duck would make>")

def openFile(obj):
    return open(str(obj), 'rU')