[Python-3000] Confused about getattr() and special methods (original) (raw)

Thomas Heller theller at ctypes.org
Tue Sep 4 11:34:46 CEST 2007

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I was looking into the Lib\test\test_uuid on Windows, which fails with this traceback:

test test_uuid failed -- Traceback (most recent call last): File "C:\buildbot\work\3.0.heller-windows\build\lib\test\test_uuid.py", line 323, in test_ipconfig_getnode node = uuid._ipconfig_getnode() File "C:\buildbot\work\3.0.heller-windows\build\lib\uuid.py", line 376, in _ipconfig_getnode for line in pipe: TypeError: '_wrap_close' object is not iterable

The test can be fixed with this little patch:

Index: Lib/os.py

--- Lib/os.py (revision 57827) +++ Lib/os.py (working copy) @@ -664,6 +664,8 @@ return self._proc.wait() << 8 # Shift left to match old behavior def getattr(self, name): return getattr(self._stream, name)

def iter(self):
```
   return iter(self._stream)
```

Supply os.fdopen() (used by subprocess!)

def fdopen(fd, mode="r", buffering=-1):

However, looking further into this I'm getting confused. Shouldn't the getattr implementation find the iter method of the _stream instance variable?

Consider this code:


##__metaclass__ = type

class X:
    def str(self):
        return "foo"
    def len(self):
        return 42
    def iter(self):
        return iter([1, 2, 3])
class proxy:
    def init(self):
        self.x = X()
    def getattr(self, name):
        return getattr(self.x, name)
p = proxy()
print(len(p))
print(str(p))
print(iter(p))


In Python2.5 and trunk, all the calls len(p), str(p), and iter(p) return the attributes
of the X class instance.  Uncommenting the 'metaclass = type' line makes the code fail.
IIUC, in py3k, classic classes do not exist any longer, so the metaclass line
has no effect anyway.  Is this behaviour intended?
Thomas


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