How to get Windows window names with ctypes in python

Question

I try to get Windows window title names and pids through handles with long objects. My code works but there is something wrong with it. I get only 4 window titles when I should get 10 or more. Can anyone help and tell me how to fix this code? I think the problem is with how I convert long objects (I don't understand them too well, as well as ctypes in general).

from __future__ import print_function
from ctypes import *

psapi = windll.psapi
titles = []


# get window title from pid
def gwtfp():
    max_array = c_ulong * 4096
    pProcessIds = max_array()
    pBytesReturned = c_ulong()

    psapi.EnumProcesses(byref(pProcessIds),
                        sizeof(pProcessIds),
                        byref(pBytesReturned))

    # get the number of returned processes
    nReturned = pBytesReturned.value/sizeof(c_ulong())
    pidProcessArray = [i for i in pProcessIds][:nReturned]
    print(pidProcessArray)
    #
    EnumWindows = windll.user32.EnumWindows
    EnumWindowsProc = WINFUNCTYPE(c_bool, POINTER(c_int), POINTER(c_int))
    GetWindowText = windll.user32.GetWindowTextW
    GetWindowTextLength = windll.user32.GetWindowTextLengthW
    IsWindowVisible = windll.user32.IsWindowVisible


    for process in pidProcessArray:
        #print("Process PID %d" % process)
        if IsWindowVisible(process):
            length = GetWindowTextLength(process)
            buff = create_unicode_buffer(length + 1)
            GetWindowText(process, buff, length + 1)
            titles.append(buff.value)


gwtfp()
print(titles)

Solution

You're passing a process ID to functions that take a window handle. What you want to do is enumerate handles for the top-level windows and then map each window to a process ID.

First lets define the ctypes function prototypes to get proper type checking on function arguments. Also, use use_last_error=True to get the safest error handling via ctypes.get_last_error. A lot of Windows functions return 0 for an error, so it's convenient to have a single errcheck function for this case, such as check_zero.

from __future__ import print_function

import ctypes
from ctypes import wintypes
from collections import namedtuple

user32 = ctypes.WinDLL('user32', use_last_error=True)

def check_zero(result, func, args):    
    if not result:
        err = ctypes.get_last_error()
        if err:
            raise ctypes.WinError(err)
    return args

if not hasattr(wintypes, 'LPDWORD'): # PY2
    wintypes.LPDWORD = ctypes.POINTER(wintypes.DWORD)

WindowInfo = namedtuple('WindowInfo', 'pid title')

WNDENUMPROC = ctypes.WINFUNCTYPE(
    wintypes.BOOL,
    wintypes.HWND,    # _In_ hWnd
    wintypes.LPARAM,) # _In_ lParam

user32.EnumWindows.errcheck = check_zero
user32.EnumWindows.argtypes = (
   WNDENUMPROC,      # _In_ lpEnumFunc
   wintypes.LPARAM,) # _In_ lParam

user32.IsWindowVisible.argtypes = (
    wintypes.HWND,) # _In_ hWnd

user32.GetWindowThreadProcessId.restype = wintypes.DWORD
user32.GetWindowThreadProcessId.argtypes = (
  wintypes.HWND,     # _In_      hWnd
  wintypes.LPDWORD,) # _Out_opt_ lpdwProcessId

user32.GetWindowTextLengthW.errcheck = check_zero
user32.GetWindowTextLengthW.argtypes = (
   wintypes.HWND,) # _In_ hWnd

user32.GetWindowTextW.errcheck = check_zero
user32.GetWindowTextW.argtypes = (
    wintypes.HWND,   # _In_  hWnd
    wintypes.LPWSTR, # _Out_ lpString
    ctypes.c_int,)   # _In_  nMaxCount

Here's a function to list the visible windows. It uses a callback that's a closure over result instead of using the optional lParam argument. The latter would require casting the argument. Using a closure is simpler.

def list_windows():
    '''Return a sorted list of visible windows.'''
    result = []
    @WNDENUMPROC
    def enum_proc(hWnd, lParam):
        if user32.IsWindowVisible(hWnd):
            pid = wintypes.DWORD()
            tid = user32.GetWindowThreadProcessId(
                        hWnd, ctypes.byref(pid))
            length = user32.GetWindowTextLengthW(hWnd) + 1
            title = ctypes.create_unicode_buffer(length)
            user32.GetWindowTextW(hWnd, title, length)
            result.append(WindowInfo(pid.value, title.value))
        return True
    user32.EnumWindows(enum_proc, 0)
    return sorted(result)

For completeness, here's a function to list all process IDs. This includes processes that belong to other Windows sessions (e.g. services in session 0).

psapi = ctypes.WinDLL('psapi', use_last_error=True)

psapi.EnumProcesses.errcheck = check_zero
psapi.EnumProcesses.argtypes = (
   wintypes.LPDWORD,  # _Out_ pProcessIds
   wintypes.DWORD,    # _In_  cb
   wintypes.LPDWORD,) # _Out_ pBytesReturned

def list_pids():
    '''Return sorted list of process IDs.'''
    length = 4096
    PID_SIZE = ctypes.sizeof(wintypes.DWORD)
    while True:
        pids = (wintypes.DWORD * length)()
        cb = ctypes.sizeof(pids)
        cbret = wintypes.DWORD()
        psapi.EnumProcesses(pids, cb, ctypes.byref(cbret))
        if cbret.value < cb:
            length = cbret.value // PID_SIZE
            return sorted(pids[:length])
        length *= 2

For example:

if __name__ == '__main__':
    print('Process IDs:')
    print(*list_pids(), sep='\n')
    print('\nWindows:')
    print(*list_windows(), sep='\n')

MSDN links:

• EnumWindows
• IsWindowVisible
• GetWindowThreadProcessId
• GetWindowTextLength
• GetWindowText
• EnumProcesses