Disallow functions from being executed as default parameters of others funcs or allow them to be executed at runtime for clarity

Ideas
1

Functions that declare functions in default arguments always execute the function at the first run time.

This is confusing and results in extra code.

Maybe I’m too lazy.

I made a small botnet with different consoles and processes that are accessed through a private local network for my work. Each worker has its own dynamic console based on the custom thread name. I noticed that the printouts were always thread 0 at the beginning.

Example:

Thread name = ‘pepe’

def server_print(message, threadname = threading.current_thread().name):
    print(threadname + message)

Example result:
MainThread 0 + message

Expected result:
Pepe + message

2

I am aware that it may be poorly stated, but perhaps it is good to consider whether it is valid to allow the execution of functions as default arguments.

3

This isn’t backwards compatible, as it would prevent e.g. a frozenset to be used as default value:

def foo(bar=frozenset()):
    ...
3 Likes
4

This sounds like the same idea as Dynamic evaluation of function argument list initializer just a few threads down, which itself is the same idea as many deferred evaluation ideas that were proposed before.

1 Like
5

I think the best way to avoid a problem like this is to use a linter that will point out the problem in your editor.

3 Likes
6

As is mentioned by @sirosen in this post, pylint and flake8-bugbear provides the tool to check for these conditions and provide you a warning in your code editor (I haven’t tried them yet, but it should draw a wavy yellow line in VSCode when the conditions you configured are met).

This is not exactly the same as you requested (disallow), but should work for your use case.

1 Like
7 
def better(arg: list[int] | None = None) -> list[int]:
    if arg is None:
        arg = create_list()

    arg.append(4)
    return arg

Exactly, I ended up doing something like what you show.