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Using SendMessage in python to set text in foreground window

We have an old, legacy database that needs input from another system. SendInput method of data input into database forms is slow and unreliable, setting clipboard and then ^v is not reliable either (I have no idea why, but database interface is very old, early 2000s). After a lot of fiddling I discovered that using SendMessage to set text and then sending VK_RETURN is fast (much faster than SendInput/keybd_event) and reliable with our database. Now this code in plain C works:
HWND fghwnd = GetForegroundWindow();
DWORD threadId = GetWindowThreadProcessId(fghwnd, NULL);
DWORD myId = GetCurrentThreadId();
if (AttachThreadInput(myId, threadId, true)) {
HWND ctrl = GetFocus();
SendMessage(ctrl, WM_SETTEXT, 0, (LPARAM) sendbuf); // TESTING
PostMessage(ctrl, WM_KEYDOWN, VK_RETURN, 0);
PostMessage(ctrl, WM_KEYUP, VK_RETURN, 0);
AttachThreadInput(myId, threadId, false);
} else {
printf("\nError: AttachThreadInput failure!\n");
}
But this one in python does not:
foregroundHwnd = win32gui.GetForegroundWindow()
foregroundThreadID = win32process.GetWindowThreadProcessId(foregroundHwnd)[0]
ourThreadID = win32api.GetCurrentThreadId()
if foregroundThreadID != ourThreadID:
win32process.AttachThreadInput(foregroundThreadID, ourThreadID, True)
focus_whd = win32gui.GetFocus()
win32gui.SendMessage(focus_whd, win32con.WM_SETTEXT, None, "test text")
win32gui.PostMessage(focus_whd, win32con.WM_KEYDOWN, win32con.VK_RETURN, None)
win32gui.PostMessage(focus_whd, win32con.WM_KEYUP, win32con.VK_RETURN, None)
win32process.AttachThreadInput(foregroundThreadID, ourThreadID, False)
The trouble is, most of our new logic in python. I turned that C code into a small python module and it works, but as result now I've got dependency on Microsoft's huge compiler and a lot of fiddling with module building. I'd like to have a python-only solution.
Any ideas why this python code does not work? These system calls look the same...

Yes, AttachThreadInput failed. According to the comment here https://toster.ru/q/79336 win32process.GetWindowThreadProcessId returns wrong value, ctypes must be used. This code works:
"""
Fast "paste" implemented via calls to Windows internals, sends parameter
string and RETURN after that
Usage:
from paste import paste
paste("test")
"""
import time
import random
import string
from ctypes import windll
import ctypes
import win32con
def random_string(string_length=10):
"""Generate a random string of fixed length """
letters = string.ascii_lowercase
return ''.join(random.choice(letters) for i in range(string_length))
ERROR_INVALID_PARAMETER = 87
def paste(text_to_paste):
"""Fast "paste" using WM_SETTEXT method + Enter key"""
current_hwnd = windll.user32.GetForegroundWindow()
current_thread_id = windll.kernel32.GetCurrentThreadId()
thread_process_id = windll.user32.GetWindowThreadProcessId(current_hwnd, None)
if thread_process_id != current_thread_id:
res = windll.user32.AttachThreadInput(thread_process_id, current_thread_id, True)
# ERROR_INVALID_PARAMETER means that the two threads are already attached.
if res == 0 and ctypes.GetLastError() != ERROR_INVALID_PARAMETER:
print("WARN: could not attach thread input to thread {0} ({1})"
.format(thread_process_id, ctypes.GetLastError()))
return
focus_whd = windll.user32.GetFocus()
windll.user32.SendMessageW(focus_whd, win32con.WM_SETTEXT, None, text_to_paste)
windll.user32.PostMessageW(focus_whd, win32con.WM_KEYDOWN, win32con.VK_RETURN, None)
windll.user32.PostMessageW(focus_whd, win32con.WM_KEYUP, win32con.VK_RETURN, None)
res = windll.user32.AttachThreadInput(thread_process_id, current_thread_id, True)
if __name__ == '__main__':
time.sleep(5) # time to switch to the target
# paste random 150 char string
paste(random_string(150))

How to create video thumbnails with Python and Gstreamer

I'd like to create thumbnails for MPEG-4 AVC videos using Gstreamer and Python. Essentially:
Open the video file
Seek to a certain point in time (e.g. 5 seconds)
Grab the frame at that time
Save the frame to disc as a .jpg file
I've been looking at this other similar question, but I cannot quite figure out how to do the seek and frame capture automatically without user input.
So in summary, how can I capture a video thumbnail with Gstreamer and Python as per the steps above?

To elaborate on ensonic's answer, here's an example:
import os
import sys
import gst
def get_frame(path, offset=5, caps=gst.Caps('image/png')):
pipeline = gst.parse_launch('playbin2')
pipeline.props.uri = 'file://' + os.path.abspath(path)
pipeline.props.audio_sink = gst.element_factory_make('fakesink')
pipeline.props.video_sink = gst.element_factory_make('fakesink')
pipeline.set_state(gst.STATE_PAUSED)
# Wait for state change to finish.
pipeline.get_state()
assert pipeline.seek_simple(
gst.FORMAT_TIME, gst.SEEK_FLAG_FLUSH, offset * gst.SECOND)
# Wait for seek to finish.
pipeline.get_state()
buffer = pipeline.emit('convert-frame', caps)
pipeline.set_state(gst.STATE_NULL)
return buffer
def main():
buf = get_frame(sys.argv[1])
with file('frame.png', 'w') as fh:
fh.write(str(buf))
if __name__ == '__main__':
main()
This generates a PNG image. You can get raw image data using gst.Caps("video/x-raw-rgb,bpp=24,depth=24") or something like that.
Note that in GStreamer 1.0 (as opposed to 0.10), playbin2 has been renamed to playbin and the convert-frame signal is named convert-sample.
The mechanics of seeking are explained in this chapter of the GStreamer Application Development Manual. The 0.10 playbin2 documentation no longer seems to be online, but the documentation for 1.0 is here.

An example in Vala, with GStreamer 1.0 :
var playbin = Gst.ElementFactory.make ("playbin", null);
playbin.set ("uri", "file:///path/to/file");
// some code here.
var caps = Gst.Caps.from_string("image/png");
Gst.Sample sample;
Signal.emit_by_name(playbin, "convert-sample", caps, out sample);
if(sample == null)
return;
var sample_caps = sample.get_caps ();
if(sample_caps == null)
return;
unowned Gst.Structure structure = sample_caps.get_structure(0);
int width = (int)structure.get_value ("width");
int height = (int)structure.get_value ("height");
var memory = sample.get_buffer().get_memory (0);
Gst.MapInfo info;
memory.map (out info, Gst.MapFlags.READ);
uint8[] data = info.data;

It's an old question but I still haven't found it documented anywhere.
I found that the following worked on a playing video with Gstreamer 1.0
import gi
import time
gi.require_version('Gst', '1.0')
from gi.repository import Gst
def get_frame():
caps = Gst.Caps('image/png')
pipeline = Gst.ElementFactory.make("playbin", "playbin")
pipeline.set_property('uri','file:///home/rolf/GWPE.mp4')
pipeline.set_state(Gst.State.PLAYING)
#Allow time for it to start
time.sleep(0.5)
# jump 30 seconds
seek_time = 30 * Gst.SECOND
pipeline.seek(1.0, Gst.Format.TIME,(Gst.SeekFlags.FLUSH | Gst.SeekFlags.ACCURATE),Gst.SeekType.SET, seek_time , Gst.SeekType.NONE, -1)
#Allow video to run to prove it's working, then take snapshot
time.sleep(1)
buffer = pipeline.emit('convert-sample', caps)
buff = buffer.get_buffer()
result, map = buff.map(Gst.MapFlags.READ)
if result:
data = map.data
pipeline.set_state(Gst.State.NULL)
return data
else:
return
if __name__ == '__main__':
Gst.init(None)
image = get_frame()
with open('frame.png', 'wb') as snapshot:
snapshot.write(image)
The code should run with both Python2 and Python3, I hope it helps someone.

Use playbin2. set the uri to the media file, use gst_element_seek_simple to seek to the desired time position and then use g_signal_emit to invoke the "convert-frame" action signal.

Windows Common Item Dialog: ctypes + COM access violation

I am trying to use the ctypes module to make calls to Windows' Common Item Dialog API. The code shown below is roughly based on the steps outlined in the MSDN documentation. Its only dependency is the comtypes.GUID module.
import ctypes
from ctypes import byref, POINTER, c_int, c_long
from ctypes.wintypes import HWND, HRESULT
from comtypes import GUID
CLSID_FileOpenDialog = '{DC1C5A9C-E88A-4DDE-A5A1-60F82A20AEF7}'
IID_IFileDialog = '{42F85136-DB7E-439C-85F1-E4075D135FC8}'
#IID_IFileOpenDialog = '{D57C7288-D4AD-4768-BE02-9D969532D960}'
CLSCTX_SERVER = 5
COINIT_APARTMENTTHREADED = 2
FOS_PICKFOLDERS = 32
FOS_FORCEFILESYSTEM = 64
ole32 = ctypes.windll.ole32
CoCreateInstance = ole32.CoCreateInstance
CoInitializeEx = ole32.CoInitializeEx
CoInitializeEx(None, COINIT_APARTMENTTHREADED)
ptr = c_int()
error = CoCreateInstance(
byref(GUID(CLSID_FileOpenDialog)), None, CLSCTX_SERVER,
byref(GUID(IID_IFileDialog)), byref(ptr))
assert error == 0
ptr = ptr.value
c_long_p = ctypes.POINTER(ctypes.c_int)
print('Pointer to COM object: %s' % ptr)
vtable = ctypes.cast(ptr, c_long_p).contents.value
print('Pointer to vtable: %s' % vtable)
func_proto = ctypes.WINFUNCTYPE(HRESULT, HWND)
# Calculating function pointer offset: 3rd entry in vtable; 32-bit => 4 bytes
show_p = ctypes.cast(vtable + 3*4, c_long_p).contents.value
print('Pointer to show(): %s' % show_p)
show = func_proto(show_p)
show(0)
Everything works as intended until the first call to show(0):
WindowsError: exception: access violation reading 0xXXXXXXXX
(Output may vary.) For comparison, I have carried out the same steps in AutoHotkey_L, which has direct access to COM.
CLSID := "{DC1C5A9C-E88A-4DDE-A5A1-60F82A20AEF7}"
IID := "{42F85136-DB7E-439C-85F1-E4075D135FC8}"
ptr := ComObjCreate(CLSID, IID)
vtable := NumGet(ptr + 0, 0, "Ptr")
show := NumGet(vtbl + 0, 3 * A_PtrSize, "Ptr")
MsgBox ptr: %ptr% vtable: %vtable% show: %A_PtrSize%
DllCall(show, "Ptr", ptr, "Ptr", 44)
The resulting macro pops up an Open File dialog, as expected. The vtable pointer offsets are the same in both cases, but only the Python version throws up an access violation.
Can anyone shed some light on this?
[I apologize for not adding more hyperlinks where appropriate, but as a new user I am limited to two at a time.]
Background:
I am putting together a lightweight module which provides a native save/open file dialog for use in Python scripts. So far I have been unable to find an implementation in pure Python. Those that exist rely on UI toolkits such as Tkinter or wxPython.

Here is the solution:
COM methods take an additional parameter: The 'this' pointer. It is implicit when you call the method from C++, in C (and in ctypes) you must supply it yourself.
Change the line
func_proto = ctypes.WINFUNCTYPE(HRESULT, HWND)
into
func_proto = ctypes.WINFUNCTYPE(HRESULT, c_long, HWND)
and this line
show(0)
into
show(ptr, 0)
and your code will work.

Use Python to extract ListView items from another application

I have an application with a ListView ('SysListView32') control, from which I would like to extract data. The control has 4 columns, only textual data.
I have been playing around the following lines (found online somewhere):
VALUE_LENGTH = 256
bufferlength_int=struct.pack('i', VALUE_LENGTH)
count = win32gui.SendMessage(TargetHwnd, commctrl.LVM_GETITEMCOUNT, 0, 0)
for ItemIndex in range(count):
valuebuffer = array.array('c',bufferlength_int + " " * (VALUE_LENGTH - len(bufferlength_int)))
ListItems = win32gui.SendMessage(TargetHwnd, commctrl.LVM_GETITEMTEXT, ItemIndex, valuebuffer)
[The above code may not be entirely executable, as I stripped it from irrelevant stuff. but the gist is certainly here.]
This seems to run ok but I must be doing something wrong - I get all sorts of mostly-zeroed data buffers in return, and none of the actual text contents I was looking for.
Any suggestions?
Thanks,
Yonatan

Well, it turns out I was wrong on several points there. However it is possible to do by allocating memory inside the target process, constructing the required struct (LVITEM) there, sending the message and reading back the result from the buffer allocated in said process.
For the sake of completeness, I attach a code example for reading SysListView32 items from a foreign process, given a window handle of the control.
from win32con import PAGE_READWRITE, MEM_COMMIT, MEM_RESERVE, MEM_RELEASE,\
PROCESS_ALL_ACCESS
from commctrl import LVM_GETITEMTEXT, LVM_GETITEMCOUNT
import struct
import ctypes
import win32api
import win32gui
GetWindowThreadProcessId = ctypes.windll.user32.GetWindowThreadProcessId
VirtualAllocEx = ctypes.windll.kernel32.VirtualAllocEx
VirtualFreeEx = ctypes.windll.kernel32.VirtualFreeEx
OpenProcess = ctypes.windll.kernel32.OpenProcess
WriteProcessMemory = ctypes.windll.kernel32.WriteProcessMemory
ReadProcessMemory = ctypes.windll.kernel32.ReadProcessMemory
memcpy = ctypes.cdll.msvcrt.memcpy
def readListViewItems(hwnd, column_index=0):
# Allocate virtual memory inside target process
pid = ctypes.create_string_buffer(4)
p_pid = ctypes.addressof(pid)
GetWindowThreadProcessId(hwnd, p_pid) # process owning the given hwnd
hProcHnd = OpenProcess(PROCESS_ALL_ACCESS, False, struct.unpack("i",pid)[0])
pLVI = VirtualAllocEx(hProcHnd, 0, 4096, MEM_RESERVE|MEM_COMMIT, PAGE_READWRITE)
pBuffer = VirtualAllocEx(hProcHnd, 0, 4096, MEM_RESERVE|MEM_COMMIT, PAGE_READWRITE)
# Prepare an LVITEM record and write it to target process memory
lvitem_str = struct.pack('iiiiiiiii', *[0,0,column_index,0,0,pBuffer,4096,0,0])
lvitem_buffer = ctypes.create_string_buffer(lvitem_str)
copied = ctypes.create_string_buffer(4)
p_copied = ctypes.addressof(copied)
WriteProcessMemory(hProcHnd, pLVI, ctypes.addressof(lvitem_buffer), ctypes.sizeof(lvitem_buffer), p_copied)
# iterate items in the SysListView32 control
num_items = win32gui.SendMessage(hwnd, LVM_GETITEMCOUNT)
item_texts = []
for item_index in range(num_items):
win32gui.SendMessage(hwnd, LVM_GETITEMTEXT, item_index, pLVI)
target_buff = ctypes.create_string_buffer(4096)
ReadProcessMemory(hProcHnd, pBuffer, ctypes.addressof(target_buff), 4096, p_copied)
item_texts.append(target_buff.value)
VirtualFreeEx(hProcHnd, pBuffer, 0, MEM_RELEASE)
VirtualFreeEx(hProcHnd, pLVI, 0, MEM_RELEASE)
win32api.CloseHandle(hProcHnd)
return item_texts

If the control is in the same process as your code, it should work. If it's in a different process (as "another application" suggests), then this doesn't work (or at least it shouldn't). Check the error codes, you should get something along the lines of "permission denied": Applications can't see into each others memory.

Showing page count with ReportLab

I'm trying to add a simple "page x of y" to a report made with ReportLab.. I found this old post about it, but maybe six years later something more straightforward has emerged? ^^;
I found this recipe too, but when I use it, the resulting PDF is missing the images..

I was able to implement the NumberedCanvas approach from ActiveState. It was very easy to do and did not change much of my existing code. All I had to do was add that NumberedCanvas class and add the canvasmaker attribute when building my doc. I also changed the measurements of where the "x of y" was displayed:
self.doc.build(pdf)
became
self.doc.build(pdf, canvasmaker=NumberedCanvas)
doc is a BaseDocTemplate and pdf is my list of flowable elements.

use doc.multiBuild
and in the page header method (defined by "onLaterPages="):
global TOTALPAGES
if doc.page > TOTALPAGES:
TOTALPAGES = doc.page
else:
canvas.drawString(270 * mm, 5 * mm, "Seite %d/%d" % (doc.page,TOTALPAGES))

Just digging up some code for you, we use this:
SimpleDocTemplate(...).build(self.story,
onFirstPage=self._on_page,
onLaterPages=self._on_page)
Now self._on_page is a method that gets called for each page like:
def _on_page(self, canvas, doc):
# ... do any additional page formatting here for each page
print doc.page

I came up with a solution for platypus, that is easier to understand (at least I think it is). You can manually do two builds. In the first build, you can store the total number of pages. In the second build, you already know it in advance. I think it is easier to use and understand, because it works with platypus level event handlers, instead of canvas level events.
import copy
import io
from reportlab.platypus import SimpleDocTemplate, Paragraph, Spacer
from reportlab.lib.styles import getSampleStyleSheet
from reportlab.lib.units import inch
styles = getSampleStyleSheet()
Title = "Hello world"
pageinfo = "platypus example"
total_pages = 0
def on_page(canvas, doc: SimpleDocTemplate):
global total_pages
total_pages = max(total_pages, doc.page)
canvas.saveState()
canvas.setFont('Times-Roman', 9)
canvas.drawString(inch, 0.75 * inch, "Page %d %s" % (doc.page, total_pages))
canvas.restoreState()
Story = [Spacer(1, 2 * inch)]
style = styles["Normal"]
for i in range(100):
bogustext = ("This is Paragraph number %s. " % i) * 20
p = Paragraph(bogustext, style)
Story.append(p)
Story.append(Spacer(1, 0.2 * inch))
# You MUST use a deep copy of the story!
# https://mail.python.org/pipermail/python-list/2022-March/905728.html
# First pass
with io.BytesIO() as out:
doc = SimpleDocTemplate(out)
doc.build(copy.deepcopy(Story), onFirstPage=on_page, onLaterPages=on_page)
# Second pass
with open("test.pdf", "wb+") as out:
doc = SimpleDocTemplate(out)
doc.build(copy.deepcopy(Story), onFirstPage=on_page, onLaterPages=on_page)
You just need to make sure that you always render a deep copy of your original story. Otherwise it won't work. (You will either get an empty page as the output, or a render error telling that a Flowable doesn't fit in the frame.)