here\'s the scenario:
I foolishly forget to assign the returned object to a variable:
>>> open(\"random_file.txt\")
         
Python is a high level language. You can't (not directly anyway) mess with memory addresses so the answer is no.
The REPL however does conveniently store the result of the last expression in a magic variable _. You can fetch it from there. To quote your example. 
>>> open("/etc/passwd","r") #Oops I forgot to assign it
>>> f = _ # Not to worry. It's stored as _
>>> f
>>>