call_command reuses already loaded command causing stale class variable value usage

[MaziyarMK]

Hi,

If a custom command has custom class variables that are used in handle(), previously set values are re-used on the next call to the same command because a new instance is not initialized.

because of:

        if isinstance(app_name, BaseCommand):
            # If the command is already loaded, use it directly.
            command = app_name
        else:
            command = load_command_class(app_name, command_name)

​https://github.com/django/django/blob/8edaf07a28a3e3848ab1edbdcd2fdc25e6bd6015/django/core/management/__init__.py#L272

I have seen this cause issues when the same command is called several times in a test.

Proposed solution:
Either warn the user about defining custom class level variables, or don't re-use the initialized command, instead kill the old object and create a new one on each use. As an optimizaiton we can require this only on custom commands, and let the base commands keep using the optimized-path with cached command instance.

Bug introduced in: ​https://github.com/django/django/commit/901c3708fb8a2e51bddd37358f8e536282a8c266

[Natalia Bidart]

Hello,

Thank you for report, though the issue you are describing is how class variables work in Python. This is not a Django specific issue, perhaps you should consider storing you state-data as an instance variable instead.

If you need further help, please consider using any of the user support channels from ​this link.