assert isinstance() not for file stream parameters?

I'm writing methods in PyCharm, and I'd like to follow its hints for the way I should be structuring my code. Here I'm passing in a parameter of type file stream, could be sys.out or a file descriptor. It prompted me to include an "assert isinstance()" for the input parameter. 

    def set_stream(self,fdout):
        """
        :param fdout: 
        """ 
        assert isinstance(fdout,...) 

I was looking up what type to call it for the purposes of isinstance() and I came across  http://dobesland.wordpress.com/2007/10/07/python-isinstance-considered-useful/:

The classic example of this is python’s famous “file-like objects”, which typically implement read and/or write in the same way and are accepted by various python functions.  I believe the DB API is another well-used example of this.  In both cases, there is no common base-class, so it’s impossible to use isinstance() to check whether a particular object is, in fact, file-like or a database object.

I guess I'll leave that assert() out. The code will break reliably enough when someone tries to write to an fdout that isn't the right sort of object.