James Y Knight wrote:
On Apr 5, 2009, at 6:29 AM, Antoine Pitrou wrote:
Brian Quinlan <brian <at> sweetapp.com> writes:
I don't see why this is helpful. Could you explain why
_RawIOBase.close() calling self.flush() is useful?
I could not explain it for sure since I didn't write the Python version.
I suppose it's so that people who only override flush() automatically
get the
flush-on-close behaviour.
It seems that a separate method "_internal_close" should've been defined
to do the actual closing of the file, and the close() method should've
been defined on the base class as "self.flush(); self._internal_close()"
and never overridden.
Are you imagining something like this?
class RawIOBase(object):
def flush(self): pass
def _internal_close(self): pass
def close(self):
self.flush()
self._internal_close()
class FileIO(RawIOBase):
def _internal_close(self):
# Do close
super()._internal_close()
class SomeSubclass(FileIO):
def flush(self):
# Do flush
super().flush()
def _internal_close(self):
# Do close
super()._internal_close()
That looks pretty good. RawIOBase.close acts as the controller and
.flush() calls move up the class hierarchy.
The downsides that I see:
- you need the cooperation of your subclasses i.e. they must call
super().flush() in .flush() to get correct close behavior (and this
represents a backwards-incompatible semantic change)
- there is also going to be some extra method calls
Another approach is to get every subclass to deal with their own close
semantics i.e.
class RawIOBase(object):
def flush(self): pass
def close(self): pass
class FileIO(RawIOBase):
def close(self):
# Do close
super().close()
class SomeSubclass(FileIO):
def _flush_internal(self):
# Do flush
def flush(self):
self._flush_internal()
super().flush()
def close(self):
FileIO._flush_internal(self)
# Do close
super().close()
I was thinking about this approach when I wrote this patch:
http://bugs.python.org/file13620/remove_flush.diff
But I think I like your way better. Let me play with it a bit.
Cheers,
Brian
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