Passing a local variable outside of a function

[malonn]

I have a sort of specific question today. I want to know how, in the specific case of my code, how I can pass a function's local variable outside the function?
Code:

def folder_exists(folder):
    enum_func = ctypes.WINFUNCTYPE(wintypes.BOOL,
                                   wintypes.HWND,
                                   wintypes.LPARAM)

    def query(hwnd, lParam):
        found = 0
        length = ctypes.WinDLL('User32').GetWindowTextLengthW(hwnd) + 1
        buf = ctypes.create_unicode_buffer(length)
        ctypes.WinDLL('User32').GetWindowTextW(hwnd, buf, length)
        if buf.value == folder:
            found += 1
        return True

    worker = enum_func(query)
    ctypes.WinDLL('User32').EnumWindows(worker, None)
    print(found)

folder_exists('Downloads')

The query function needs to return true in order for the C function call "EnumWindows" to work. Basically what I'm trying to do here is 'do something' (don't worry about what) once a certain folder title is found. So how can I or what can I pass as some sort of indicator that the correct folder was found from the query function? Is there some way I can pass the found local variable outside the function? I needs to be whatever it's set to when the function is called.

[ichabod801]

What about return [found]? Since it's a non-empty list, it will evaluate as True, which should satisfy EnumWindows. However, it also contains the value you want.

[malonn]

The problem with that is the function is sort of a special case that really should only be called with the call to "EnumWindows". It won't give an accurate result otherwise and found won't be accurate.

[Gribouillis]

I don't understand the WinDLL part but you could try a callable object

def folder_exists(folder):
    enum_func = ctypes.WINFUNCTYPE(wintypes.BOOL,
                                   wintypes.HWND,
                                   wintypes.LPARAM)
    class Query:
        def __call__(self, hwnd, lParam):
            self.found = 0
            length = ctypes.WinDLL('User32').GetWindowTextLengthW(hwnd) + 1
            buf = ctypes.create_unicode_buffer(length)
            ctypes.WinDLL('User32').GetWindowTextW(hwnd, buf, length)
            if buf.value == folder:
                self.found += 1
            return True
    query = Query()
    worker = enum_func(query)
    ctypes.WinDLL('User32').EnumWindows(worker, None)
    print(query.found)
 
folder_exists('Downloads')

[malonn]

Thanks, but didn't work. found printed as 0 where it should have been 1. To clarify, it's the call enum_func that needs a boolean value to be returned from the query function, not "EnumWindows". "EnumWindows" needs the function prototype "WINFUNCTYPE".

[Gribouillis]

found printed as 0 where it should have been 1.

How do you know it should have been 1? Did the code execute the self.found += 1 ? Try to raise a RuntimeError at this point to see what it does.

[malonn]

It should be 1 because the code checks to see if a window with the title "Downloads" is open, which it is. And yes, self.found += 1 was executed.

I'm a noob, how would I raise a runtimeerror?

---

A Global will work, but from what I read, globals are bad form.

[ichabod801]

raise RuntimeError('useful message here')

[malonn]

I figured it out--thanks, ichabod & Gribouillis. I ended up using nested functions and nonlocal. Here's the code for any interested:

def get_folder(name_in):
    folder = ''
    enum_func = ctypes.WINFUNCTYPE(wintypes.BOOL,
                                   wintypes.HWND,
                                   wintypes.LPARAM)

    def names_callback(hwnd, lParam):
        nonlocal folder
        length = ctypes.WinDLL('User32').GetWindowTextLengthW(hwnd) + 1
        buf = ctypes.create_unicode_buffer(length)
        ctypes.WinDLL('User32').GetWindowTextW(hwnd, buf, length)
        if buf.value == name_in:
            folder = name_in
        return 1

    worker = enum_func(names_callback)
    ctypes.WinDLL('User32').EnumWindows(worker, None)
    return folder