Where does the function for os.walk onerror return to? How do I add more arguments to the onerror function call?

Question

Im writing a program to walk a filesystem using os.walk.

I have my for loop using os.walk, and onerror function as follows:

def walk_error(os_error):

    return(os_error)

def main():

    for root, dirs, files in os.walk('/var/spool/cron/', onerror=walk_error):

    print(root, dirs, files)

Where does that return statement from the onerror function go to? How do I reference it? I can certainly just do print(os_error) in my walk_error function and it will work fine. But I want to save that error somewhere.

How do I, say, add a list as an argument to the error handling function aswell, so I can append that error to a list of my failed directories?

For example:

def walk_error(os_error, list_of_errors):
    list_of_errors.append(os_error)

That would work great! But unfortunately it doesnt seem you can do that type of a function call with multiple arguments in the onerror call.

Or how do I assign that returned value to a variable to do that in my main function? That os_error is being "returned" but its not returned to any of the 3 tuples that os.walk generates. Is there a way to reference that returned value in main()?

How do I do more complicated error handling here?

Answer 1

Use an inner function (aka closure):

def main():

    list_of_errors = []

    def walk_error(os_error):
        list_of_errors.append(os_error)

    for root, dirs, files in os.walk('/var/spool/cron/', onerror=walk_error):
        print(root, dirs, files)