Under 3.2 and 3.1:

>>> with open("foo", "wb") as x: pass
... 
>>> with open("foo", "wb") as (x, y): pass
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
io.UnsupportedOperation: read

Similar oddities under 2.7:

>>> with open("foo", "wb") as (x, y): pass
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: File not open for reading
>>> with io.open("foo", "wb") as (x, y): pass
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
io.UnsupportedOperation: read

Of course, you get the same error with:

>>> f = open('foo', 'wb')
>>> x, y = f
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: File not open for reading

i.e. the tuple assignment iterates over the file, and calls readline()

I would say it's strange but correct. (and unavoidable I think)

At least not without losing generality, and we don't like that.