The attribute's action of an object is not correct.

[Yongyang]

BPO	5620

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2009-04-01.13:05:28.941>
created_at = <Date 2009-03-31.11:27:23.882>
labels = ['type-bug']
title = "The attribute's action of an object is not correct."
updated_at = <Date 2009-04-01.13:05:28.917>
user = 'https://bugs.python.org/Yongyang'

bugs.python.org fields:

activity = <Date 2009-04-01.13:05:28.917>
actor = 'Yong yang'
assignee = 'none'
closed = True
closed_date = <Date 2009-04-01.13:05:28.941>
closer = 'Yong yang'
components = ['None']
creation = <Date 2009-03-31.11:27:23.882>
creator = 'Yong yang'
dependencies = []
files = []
hgrepos = []
issue_num = 5620
keywords = []
message_count = 3.0
messages = ['84765', '84791', '85003']
nosy_count = 2.0
nosy_names = ['Kozyarchuk', 'Yong yang']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue5620'
versions = ['Python 3.0']

[Yongyang]

The following is the test code.

class C1:
	myurl = []	
	def test(self):
		url = [5,6,7]
		self.myurl.extend(url)		
def testv():
	c = C1()
	c.test()
	print(c.myurl)
	
i = 0
while i<10 :
	testv()
	i = i+1

The output is :

[5, 6, 7]
[5, 6, 7, 5, 6, 7]
[5, 6, 7, 5, 6, 7, 5, 6, 7]
[5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7]
[5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7]
[5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7]
[5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7]
[5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6,
7]
[5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6,
7, 5, 6, 7]
[5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6, 7, 5, 6,
7, 5, 6, 7, 5, 6, 7]

The myurl of class C1 is not set to [] when a new object is created.
All objects use the same memory.

[Kozyarchuk]

AFAIK, This is expected behavior. myurl is a class attribute if you
want it to be different per instance you should re-initialize it in the
__init__ method. See below.

>>> class C1(object):
...     def __init__(self):
...             self.myurl = []
...     def test(self):
...             self.myurl.extend([5,6,7])
...
[44085 refs]
>>> def testv():
...     c = C1()
...     c.test()
...     print(c.myurl)
...
[44108 refs]
>>> for i in range(10):
...     testv()
...
[5, 6, 7]
[5, 6, 7]
[5, 6, 7]
[5, 6, 7]
[5, 6, 7]
[5, 6, 7]
[5, 6, 7]
[5, 6, 7]
[5, 6, 7]
[5, 6, 7]
[44119 refs]

[Yongyang]

Thanks a lot!
Kozyarchuk.

I have thought the self.myurl should be the object variable, not class
variable.
The class variable really is confusing.

Why do they like that?