| msg32076 - (view) |
Author: David Benbennick (dbenbenn) |
Date: 2007-05-19 14:03 |
| Consider the following code: >>> class foo(set): ... def __init__(self, iter): ... print "foo.__init__" ... set.__init__(self, iter) ... >>> x = foo([1,2]) foo.__init__ >>> y = foo([2,3]) foo.__init__ >>> x & y foo([2]) As you can see, the foo.__and__ method creates a new foo object without calling foo.__init__. The problem is in Objects/setobject.c:make_new_set(). |
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| msg32077 - (view) |
Author: Georg Brandl (georg.brandl) *  |
Date: 2007-05-19 16:11 |
| Wasn't that fixed some time ago? @OP: what Python version do you use? |
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| msg32078 - (view) |
Author: Raymond Hettinger (rhettinger) * |
Date: 2007-05-19 16:25 |
| Sorry, this is just the way Python works. Given that the __and__ operation has no way of knowing the signature of your subclass contructor, it will produce a new set from your two foo inputs. This design prevades the language (for example list and int have similar behaviors). Recommend closing this as not-a-bug: >>> class foo(list): def __init__(self, iter): print 'foo.__init__' list.__init__(self, iter) >>> x = foo([1,2]) foo.__init__ >>> y = foo([2,3]) foo.__init__ >>> x + y [1, 2, 2, 3] >>> type(_) <type 'list'> >>> >>> class foo(int): pass >>> foo(1) + foo(2) 3 >>> type(_) <type 'int'> |
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| msg32079 - (view) |
Author: Georg Brandl (georg.brandl) * |
Date: 2007-05-19 16:32 |
| There is a difference: in the list and int case, the new object is of the base type. In the set case, the new object is of type foo. But the constructor signature argument is a valid one. |
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| msg32080 - (view) |
Author: Raymond Hettinger (rhettinger) * |
Date: 2007-05-19 16:40 |
| Hmm, that's a bummer. It is probably going to have to change. Will look it and fix it when I get a chance. |
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| msg64319 - (view) |
Author: Raymond Hettinger (rhettinger) * |
Date: 2008-03-22 12:14 |
| Attaching a possible fix (untested). |
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| msg75932 - (view) |
Author: Raymond Hettinger (rhettinger) * |
Date: 2008-11-16 11:15 |
| Improved solution attached. |
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| msg75933 - (view) |
Author: Raymond Hettinger (rhettinger) * |
Date: 2008-11-16 11:47 |
| Fixed in r67232. Don't think this should be backported to the 2.x series as it may break working code relying on the old behavior. |
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