[ python-Bugs-1583060 ] class member inconsistancies

Mon Oct 23 20:13:38 CEST 2006

Bugs item #1583060, was opened at 2006-10-23 14:13
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Category: Type/class unification
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: EricDaigno (santaroga)
Assigned to: Nobody/Anonymous (nobody)
Summary: class member inconsistancies

Initial Comment:
Hi...  When coding rapid classes I stumbled upon a
strange behaviour in the way python deals with data
membership of it's instances (new style) when using C
struct like container classes

behaviour changes when data members are declared in the
class itself as opposed to be declared in the __init__
method...

I understand that python does not perform any sort of
initialization outside of __init__ but this really
create confusion as to what is allowed and what is not
and is clear inconstancy that is either a language
usability bug of a plain buf in class
creation-initialization.

The problem happens when declaring a class that does
not contain __init__ method override but contains a
bunch of data elements that are initialized in the
declaration.

Expected behaviour would be that when a new instance is
created the python interpreter would create a new
instance and initialize the members as stated in the
class declaration and then call the __init__ method
(from object or the overriden __init__ from the class)

The reality is quite different.

Immutables (string) are dealt with correctly but
mutables (list, dict) are initialized only once.  Every
subsequent instantiation of the class will therefore
see new instances of member immutables objects but will
SHARE instances of the member mutables.

I have created a small programm that illustrate the
behaviour :

------------------------------------------------CodeStart

class A(object):
    def __init__(self):

        self.argsList = []
        self.dictArgs = {}
        self.ARG1 = ""
        self.ARG2 = ""

    def multUnnammedArgs(self,
                         *argsList):
        if not argsList is None:
            self.argsList += argsList

    def multNAmmedArgument(self,
                           **argDict):
        if not argDict is None:
            for i in argDict.iteritems():
                self.dictArgs[i[0]] = i[1]

    def mixedArguments(self, 
                       ARG1,
                       ARG2,
                       *argList,
                       **argDict):
        self.ARG1 = ARG1
        self.ARG2 = ARG2

        self.multUnnammedArgs(*argList)

        self.multNAmmedArgument(**argDict)

    def __str__(self):
        string = "Object A :"
        string += "\n\t\tARG1=" + self.ARG1 
        string += "\n\t\tARG2=" + self.ARG2 
        string += "\n\tUnnammed Arguments"
        for a in self.argsList:
            string += "\n\t\t" + a

        string += "\n\tNamed Arguments"
        for a in self.dictArgs.iteritems():
            string += "\n\t\t" + a[0] + "=" + a[1]

        return string

if __name__ == '__main__':
    obj = A()

    obj.multUnnammedArgs("arg1", "arg2", "arg3")
    print obj

    obj.multNAmmedArgument(TOTO = "toto",
                           TITI = "titi",
                           TaTa = "tATa")

    print obj   
    obj.mixedArguments(ARG1="ZeArg1",
                       ARG2="ZeArg2",
                       TOTO2 = "toto2",
                       TITI2 = "titi2",
                       TaTa2 = "tATa2")
    print obj     

-----------------------------------------------Code End

Here is the dump of my python environment 

---------------------------------------------Dump Start
[eric at speigel ~]$ python -v
# installing zipimport hook
import zipimport # builtin
# installed zipimport hook
# /lesia/toolbox/python/lib/python2.4/site.pyc matches
/lesia/toolbox/python/lib/python2.4/site.py
import site # precompiled from
/lesia/toolbox/python/lib/python2.4/site.pyc
# /lesia/toolbox/python/lib/python2.4/os.pyc matches
/lesia/toolbox/python/lib/python2.4/os.py
import os # precompiled from
/lesia/toolbox/python/lib/python2.4/os.pyc
import posix # builtin
# /lesia/toolbox/python/lib/python2.4/posixpath.pyc
matches /lesia/toolbox/python/lib/python2.4/posixpath.py
import posixpath # precompiled from
/lesia/toolbox/python/lib/python2.4/posixpath.pyc
# /lesia/toolbox/python/lib/python2.4/stat.pyc matches
/lesia/toolbox/python/lib/python2.4/stat.py
import stat # precompiled from
/lesia/toolbox/python/lib/python2.4/stat.pyc
# /lesia/toolbox/python/lib/python2.4/UserDict.pyc
matches /lesia/toolbox/python/lib/python2.4/UserDict.py
import UserDict # precompiled from
/lesia/toolbox/python/lib/python2.4/UserDict.pyc
# /lesia/toolbox/python/lib/python2.4/copy_reg.pyc
matches /lesia/toolbox/python/lib/python2.4/copy_reg.py
import copy_reg # precompiled from
/lesia/toolbox/python/lib/python2.4/copy_reg.pyc
# /lesia/toolbox/python/lib/python2.4/types.pyc matches
/lesia/toolbox/python/lib/python2.4/types.py
import types # precompiled from
/lesia/toolbox/python/lib/python2.4/types.pyc
# /lesia/toolbox/python/lib/python2.4/warnings.pyc
matches /lesia/toolbox/python/lib/python2.4/warnings.py
import warnings # precompiled from
/lesia/toolbox/python/lib/python2.4/warnings.pyc
# /lesia/toolbox/python/lib/python2.4/linecache.pyc
matches /lesia/toolbox/python/lib/python2.4/linecache.py
import linecache # precompiled from
/lesia/toolbox/python/lib/python2.4/linecache.pyc
import encodings # directory
/lesia/toolbox/python/lib/python2.4/encodings
#
/lesia/toolbox/python/lib/python2.4/encodings/__init__.pyc
matches
/lesia/toolbox/python/lib/python2.4/encodings/__init__.py
import encodings # precompiled from
/lesia/toolbox/python/lib/python2.4/encodings/__init__.pyc
# /lesia/toolbox/python/lib/python2.4/codecs.pyc
matches /lesia/toolbox/python/lib/python2.4/codecs.py
import codecs # precompiled from
/lesia/toolbox/python/lib/python2.4/codecs.pyc
import _codecs # builtin
#
/lesia/toolbox/python/lib/python2.4/encodings/aliases.pyc
matches
/lesia/toolbox/python/lib/python2.4/encodings/aliases.py
import encodings.aliases # precompiled from
/lesia/toolbox/python/lib/python2.4/encodings/aliases.pyc
#
/lesia/toolbox/python/lib/python2.4/encodings/utf_8.pyc
matches
/lesia/toolbox/python/lib/python2.4/encodings/utf_8.py
import encodings.utf_8 # precompiled from
/lesia/toolbox/python/lib/python2.4/encodings/utf_8.pyc
Python 2.4.2 (#1, Aug  1 2006, 16:57:48)
[GCC 4.0.2 20051125 (Red Hat 4.0.2-8)] on linux2
Type "help", "copyright", "credits" or "license" for
more information.
dlopen("/lesia/toolbox/python/lib/python2.4/lib-dynload/readline.so",
2);
import readline # dynamically loaded from
/lesia/toolbox/python/lib/python2.4/lib-dynload/readline.so
>>>
-------------------------------------------Dump end

----------------------------------------------------------------------

You can respond by visiting: 
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