A list in a class seems to be static?

Asked Jan 08 '18 at 23:29

Active Jan 09 '18 at 00:36

Viewed 24 times

In a Python class I wrote the following method:

class user():
    address_list = []

    def __init__(self):
        self.address_list.append("a")

When I use it as this:

ur1 = user()
ur1.address_list.append("b")
ur2 = user()
ur2.address_list.append("c")
ur2.address_list.append("d")

print("user1's address: ", len(ur1.address_list))
print("user2's address: ", len(ur2.address_list))

The output was:

user1's address: 5
user2's address: 5

But my expectation was:

user1's address: 2   #a, b
user2's address: 3   #a,c,d

What's wrong with my code?

edited Jan 09 '18 at 00:36

martineau

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asked Jan 08 '18 at 23:29

Grant Huang

You indentation is wrong. Try indenting address_list and init to be in the same block as the class. – AmourK Jan 08 '18 at 23:31
All your `user` instances share a single `address_list`. Move `self.address_list = []` to the `__init__` – Patrick Haugh Jan 08 '18 at 23:32
2

Yes, it is static, it's a class attribute, not an instance attribute. – Peter Wood Jan 08 '18 at 23:32
Do print the user's address together, you'll see the problem. `__init__` is appending 'a' twice thus the 5. – progmatico Jan 08 '18 at 23:32
@PatrickHaugh yes. move the self.address_list = [] into the constuctor is ok. Thanks. – Grant Huang Jan 08 '18 at 23:47

A list in a class seems to be static?

0 Answers0