Catching key events globally

Ram_Rachum · July 26, 2015, 3:17pm

Hi everyone,

There’s something I’m trying to do with wxPython and I can’t figure out how.

I want to catch key events globally. This means key-up, key-down and char events. (I’m trying to build something like AHK in Python.)

Now, I know wxPython allows global hotkeys, but that’s not satisfactory, because I want to get all the events, including key up, key down and char. How can I do that?

(I tried using pyHook, which almost worked except char events aren’t implemented.)

Thanks,

Ram.

Ram_Rachum · July 26, 2015, 7:15pm

I should specify: I’m on Windows 7 and I’m okay with a Windows-only solution.

···

On Sunday, July 26, 2015 at 6:17:01 PM UTC+3, Ram Rachum wrote:

Hi everyone,

There’s something I’m trying to do with wxPython and I can’t figure out how.

I want to catch key events globally. This means key-up, key-down and char events. (I’m trying to build something like AHK in Python.)

Now, I know wxPython allows global hotkeys, but that’s not satisfactory, because I want to get all the events, including key up, key down and char. How can I do that?

(I tried using pyHook, which almost worked except char events aren’t implemented.)

Thanks,

Ram.

Tim_Roberts · July 27, 2015, 6:25pm

Ram Rachum wrote:

There's something I'm trying to do with wxPython and I can't figure
out how.

I want to catch key events globally. This means key-up, key-down and
char events. (I'm trying to build something like AHK in Python.)

Now, I know wxPython allows global hotkeys, but that's not
satisfactory, because I want to get all the events, including key up,
key down and char. How can I do that?

(I tried using pyHook, which almost worked except char events aren't
implemented.)

A Windows hook is the right solution. You shouldn't need WM_CHAR
events. All keystrokes arrive as WM_KEYDOWN and WM_KEYUP. The default
handler for WM_KEYDOWN will generate a WM_CHAR if it is appropriate for
the key that was pressed. You can get everything you need from the key
down and up sequences.

···

--
Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

cool-RR · July 27, 2015, 7:13pm

Hi Tim,

I’m not sure how to follow your solution.

“A Windows hook is the right solution.” So you mean I shouldn’t use wxPython? Or is there a way to do a global Windows hook for char events in wxPython? If not how can I do this?

“You can get everything you need from the key down and up sequences.” Are you sure? Because I understand that the OS has its own logic for char events. For example, if I press alt-x then it generates a key down event but not a key char event, because a character isn’t emitted. Another thing is that non-US keyboards have different characters and their contained in the key char event but not the key down event.

Thanks for your help,

Ram Rachum.

···

On Mon, Jul 27, 2015 at 9:25 PM, Tim Roberts timr@probo.com wrote:

Ram Rachum wrote:

There’s something I’m trying to do with wxPython and I can’t figure

out how.

I want to catch key events globally. This means key-up, key-down and

char events. (I’m trying to build something like AHK in Python.)

Now, I know wxPython allows global hotkeys, but that’s not

satisfactory, because I want to get all the events, including key up,

key down and char. How can I do that?

(I tried using pyHook, which almost worked except char events aren’t

implemented.)

A Windows hook is the right solution. You shouldn’t need WM_CHAR

events. All keystrokes arrive as WM_KEYDOWN and WM_KEYUP. The default

handler for WM_KEYDOWN will generate a WM_CHAR if it is appropriate for

the key that was pressed. You can get everything you need from the key

down and up sequences.

–

Tim Roberts, timr@probo.com

Providenza & Boekelheide, Inc.

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Tim_Roberts · July 27, 2015, 10:55pm

I mean that pyHook will allow you to create a global Windows hook in
Python. It should do what you need to do.
It depends on what you need to do with the information. The Windows
keyboard hooks – even at the API level – only deliver key down and
key up. You can look that up in MSDN under the WH_KEYBOARD hook
type.
Every key event starts with a key down. From the key down info, the
input subsystem can create a char event, if the current keyboard
state warrants it. A keyboard hook can’t get that info, but you can
certainly get the same key info that the system got.

···

Ram Rachum wrote:

      "A Windows hook is the right solution." So you mean I
shouldn’t use wxPython? Or is there a way to do a global Windows
hook for char events in wxPython? If not how can I do this?

      "You can get everything you need from the key down and up
sequences." Are you sure? Because I understand that the OS has
its own logic for char events. For example, if I press alt-x
then it generates a key down event but not a key char event,
because a character isn’t emitted. Another thing is that
non-US keyboards have different characters and their contained
in the key char event but not the key down event.

-- Tim Roberts, Providenza & Boekelheide, Inc.

timr@probo.com

cool-RR · July 28, 2015, 10:05am

Ram Rachum wrote:

"A Windows hook is the right solution." So you mean I shouldn't use
wxPython? Or is there a way to do a *global *Windows hook for char events
in wxPython? If not how can I do this?

I mean that pyHook will allow you to create a global Windows hook in
Python. It should do what you need to do.

PyHook doesn't support char events. From the docs:

    def SubscribeKeyChar(self, func):
        '''
        Registers the given function as the callback for this keyboard
event type.
        Use the KeyChar property as a shortcut.

B{Note}: this is currently non-functional, no WM_*CHAR messages are
processed by the keyboard hook.

        @param func: Callback function
        @type func: callable
        '''

"You can get everything you need from the key down and up sequences."
Are you sure? Because I understand that the OS has its own logic for char
events. For example, if I press alt-x then it generates a key down event
but not a key char event, because a character isn't emitted. Another thing
is that non-US keyboards have different characters and their contained in
the key char event but not the key down event.

It depends on what you need to do with the information. The Windows
keyboard hooks -- even at the API level -- only deliver key down and key
up. You can look that up in MSDN under the WH_KEYBOARD hook type.

One thing I want to do is get all the typed text.

Every key event starts with a key down. From the key down info, the input
subsystem can create a char event, if the current keyboard state warrants
it. A keyboard hook can't get that info, but you can certainly get the
same key info that the system got.

I can get all the keydown events and try to recreate the char events, but
then I need to reimplement logic like checking whether the alt-key was
pressed, or checking the user language and translating the keypress to a
character in their language, and possibly lots of other logic I'm not
thinking about. A much better solution would be to get those char events
directly, after the system has already applied all that logic. The question
is how do I get that info.

···

On Tue, Jul 28, 2015 at 1:55 AM, Tim Roberts <timr@probo.com> wrote:

--
Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

--
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Tim_Roberts · July 29, 2015, 6:59pm

Right, because Windows itself does support char events in system
hooks.
Key down and key up will do that, with a little additional work.
That’s a much easier solution for YOU, but it’s not a much better
solution for the system. Much of that logic happens in the process
of the application that is to receive the message. The input system
deals in key up and key down.
Have you done any reading at all about the window hook concept at
the API level? PyHook isn’t inventing any capabilities that aren’t
in the system. There are other hook types available. For example,
you can install a hook that gets called every time an application
pulls a message from its message queue. That would certainly get
you WM_CHAR messages, but that requires that your hook code be in a
DLL, because the DLL has to be injected into every process in the
system. That’s a heavyweight operation, and it cannot be done in
Python.

···

Ram Rachum wrote:

        On Tue, Jul 28, 2015 at 1:55 AM, Tim
Roberts timr@probo.com wrote:

Ram Rachum wrote:

                    "A Windows hook is the right solution." So
you mean I shouldn’t use wxPython? Or is there a
way to do a global Windows hook for
char events in wxPython? If not how can I do
this?

I mean that pyHook will allow you to create a
global Windows hook in Python. It should do what you
need to do.

PyHook doesn’t support char events. From the docs:

            It depends on what
you need to do with the information. The Windows
keyboard hooks – even at the API level – only deliver
key down and key up. You can look that up in MSDN under
the WH_KEYBOARD hook type.

One thing I want to do is get all the typed text.

            Every key event
starts with a key down. From the key down info, the
input subsystem can create a char event, if the current
keyboard state warrants it. A keyboard hook can’t get
that info, but you can certainly get the same key info
that the system got.

          I can get all the keydown events and try to recreate
the char events, but then I need to reimplement logic like
checking whether the alt-key was pressed, or checking the
user language and translating the keypress to a character
in their language, and possibly lots of other logic I’m
not thinking about. A much better solution would be to get
those char events directly, after the system has already
applied all that logic. The question is how do I get that
info.

-- Tim Roberts, Providenza & Boekelheide, Inc.

timr@probo.com