testing for a network connection

[Gribouillis]

I don't know if this is possible in general, but it looks like bad design. Friendly python functions that receive a file with a write() method will usually accept any file-like object and will never try to guess what's beyond the write method. I think if you need the information, give the responsibility to the caller and change the signature to

def flood_with_spam(file, is_network):
    pass