Populating instances of class automatically

[Daugeras]

BPO	35339
Nosy	@Wooble

^{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 2018-11-29.06:41:01.471>
created_at = <Date 2018-11-28.17:05:42.662>
labels = ['invalid', 'type-bug', '3.7']
title = 'Populating instances of class automatically'
updated_at = <Date 2018-11-29.06:41:01.470>
user = 'https://bugs.python.org/Daugeras'

bugs.python.org fields:

activity = <Date 2018-11-29.06:41:01.470>
actor = 'steven.daprano'
assignee = 'none'
closed = True
closed_date = <Date 2018-11-29.06:41:01.471>
closer = 'steven.daprano'
components = []
creation = <Date 2018-11-28.17:05:42.662>
creator = 'Daugeras'
dependencies = []
files = []
hgrepos = []
issue_num = 35339
keywords = []
message_count = 3.0
messages = ['330613', '330614', '330630']
nosy_count = 2.0
nosy_names = ['geoffreyspear', 'Daugeras']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue35339'
versions = ['Python 3.7']

[Daugeras]

Hello, I am not sure it is a bug, but it is a very strange behavior of Python, which I do not understand.

I created a class (mainly a structure) and instantiated an object of this class in a first function (Object 1). The function populates Object 1.
In another function, I instantiate another object of the same class (Object 2) , and Object 2 is automatically populated with the data of Object 1. Note than Object 1 and Object 2 have different memory adresses.

This behavior is very strange. Is it normal for Python or is it a Bug ?

[Wooble]

It's impossible to guess exactly what you did from your vague description instead of actual code, but it may be covered by this FAQ question: https://docs.python.org/3/faq/programming.html#why-are-default-values-shared-between-objects

(mutable objects as class rather than instance attributes will display similar behavior. This isn't a bug.)

[Daugeras]

Hi Geoffrey,

Indeed you where right, this is not a bug.
The link you provided did solve my problem.
I declared classes with attributes as strings, lists, etc... and indeed it was the reason for the issue.
I changed it to instantiate the attributes in the __init__ method of the class, and it solved the problems.
Thanks again !!