Issue 1012249: dictionary referencing error (original) (raw)

Issue1012249

Created on 2004-08-19 14:57 by ckbcouture, last changed 2022-04-11 14:56 by admin. This issue is now closed.

Messages (5)
msg22136 - (view)	Author: AMIT Consulting LLC (ckbcouture)	Date: 2004-08-19 14:57
When I write a class as such: class MyObject: myDict = {} ... Each new instance refers to the SAME dictionary, not a newly minted one. However, this does not hold true for other data types. This has forced me to place dictionary declarations in the __init__ method to ensure uniqueness. Unless this is intended for some obscure reason, it should be fixed. Thanks, Cameron
msg22137 - (view)	Author: Raymond Hettinger (rhettinger) *	Date: 2004-08-19 16:00
Logged In: YES user_id=80475 That is the intended behavior. Attribute definitions inside the class definition but outside the method definitions are essentially class variables. They are useful because each instance does not need to have its own copy. For cases where an instance needs its own copy, your solution using __init__ was the right thing to do. In time, this will be obvious and all will feel as right as rain.
msg22138 - (view)	Author: AMIT Consulting LLC (ckbcouture)	Date: 2004-08-19 16:09
Logged In: YES user_id=1096248 The problem is that this only seems to work for dictionaries, tuples and lists. it DOES NOT work for numbers and strings. Try the following: class Test: mint = 1 mchar = "A" mdict = {} mlist = [] mtup = () def __init__( self ): self.mint += 1 self.mchar += self.mchar self.mdict[ self.mchar ] = self.mint self.mlist.append( self.mdict ) self.mtup += ( self.mlist, ) print self.mtup for i in range(10): Test() For me it outputs: ([{'AA': 2}],) ([{'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) Which means that it is working as you say for some, but not all data types. Is THAT intended? Thanks, Cameron
msg22139 - (view)	Author: AMIT Consulting LLC (ckbcouture)	Date: 2004-08-19 16:20
Logged In: YES user_id=1096248 The problem is that this only seems to work for dictionaries, tuples and lists. it DOES NOT work for numbers and strings. Try the following: class Test: mint = 1 mchar = "A" mdict = {} mlist = [] mtup = () def __init__( self ): self.mint += 1 self.mchar += self.mchar self.mdict[ self.mchar ] = self.mint self.mlist.append( self.mdict ) self.mtup += ( self.mlist, ) print self.mtup for i in range(10): Test() For me it outputs: ([{'AA': 2}],) ([{'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) ([{'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}, {'AA': 2}],) Which means that it is working as you say for some, but not all data types. Is THAT intended? Thanks, Cameron
msg22140 - (view)	Author: Raymond Hettinger (rhettinger) *	Date: 2004-08-19 17:14
Logged In: YES user_id=80475 This is also the way it is supposed to be. At issue is whether the object is mutable or not. If mutable, something like .append() alters the object inplace (at the class level). If immutable, something like a = a + b reads a from the class level, adds b creating a newobject, and stores the new object, a, back at the instance level. Please work through the tutorial or make a newsgroup posting requesting better explanations. This isn't a bug, it is just something intrinsic to Python and is a minor step that everyone has to go through on the path to mastering the language.