Class instances store different values than originally given

Asked Dec 28 '19 at 13:39

Active Dec 28 '19 at 13:39

Viewed 26 times

I have a problem in my current project and i narrowed down the problem to this.

I want this output: 0, 1, 2, 3, 4, 5, ...

But my output: 9, 9, 9, 9, 9, 9, ...

class Foo:
    def __init__(self, command):
        self.command = command


listOfFoos = []

for i in range(10):
    listOfFoos.append(Foo(command=(lambda: print(i))))

for foo in listOfFoos:
    foo.command()

asked Dec 28 '19 at 13:39

Dilan Boskan

Have a look at this https://docs.python-guide.org/writing/gotchas/#mutable-default-arguments – Tom Wojcik Dec 28 '19 at 13:40
1

Does this answer your question? ["Least Astonishment" and the Mutable Default Argument](https://stackoverflow.com/questions/1132941/least-astonishment-and-the-mutable-default-argument) – Tom Wojcik Dec 28 '19 at 13:41
Lambdas have late binding. So the reference to `i` will refer to the last value of `i` in the loop which is 9. – N Chauhan Dec 28 '19 at 13:45
N Chauhan how can i work around this? – Dilan Boskan Dec 28 '19 at 13:47
1

`command=lambda x=i:print(x)` – furas Dec 28 '19 at 15:14

Class instances store different values than originally given

0 Answers0