Opening a file in Python

I'm sure I read this somewhere recently, but my scratchy memory and command of Google can't bring it back to me.

Is there a Python idiom for accepting either a file name or a file object as a function parameter?

The closest I can get is this;

def my_function(file_name_or_object):

try:

    open(file_name_or_object)

except TypeError:

    file = file_name_or_object

return file

Any improvements on this are more than welcome.