size=None and unsizable=False are used together, should we remove both? And please make sure that no one calls ResponseStreamReader with the removed kwargs.

Or maybe keep those two but improve conditional logic. However, we still need to make sure that int(size) does not throw exceptions (or we need to catch them when that happens). Whether size is of type int or string makes a difference.

elif not unsizable and size is not None:
    try:
        elf._size = int(size)
    except:
        elf._size = None

So after a little research I've found the unsizable argument is never used, and the size argument is used, but seems to usually be None, so I've decided to change the code to match the suspected intention of original writer. When a size is given the stream will read to that size, if it is None, the whole stream will be read.

 def __init__(self, response, size=None, name=None):
        super().__init__()
        if 'Content-Length' in response.headers:
            self._size = int(response.headers['Content-Length'])
        else:
            self._size = size

        self._name = name
        self.response = response