How to detect that a key is being pressed, not HAS been pressed earlier!??

[Rune]

Hey

I'm trying to build a gui application and need to know if the user is
actually holding down the shift or ctrl key. That is, if the user
currently is holding down the shift key. In pseudo code this will boil
down to something like this:

def test:
if user presses shift:
return SHIFT_IS_PRESSED
elif user presses ctrl:
return CTRL_IS_PRESSED
else
return false

It's important to notice here that I'm not interested if the user has
already pressed shift or ctrl. I'm only interested in knowing if he is
currently holding down one of these keys. (I have looked into msvcrt
and the like but have found no answer..) The function should also work
in both windows and Linux.

Any help is appriciated

 

[Gilles Lenfant]

Hey

I'm trying to build a gui application and need to know if the user is
actually holding down the shift or ctrl key. That is, if the user
currently is holding down the shift key. In pseudo code this will boil
down to something like this:

def test:
if user presses shift:
return SHIFT_IS_PRESSED
elif user presses ctrl:
return CTRL_IS_PRESSED
else
return false

It's important to notice here that I'm not interested if the user has
already pressed shift or ctrl. I'm only interested in knowing if he is
currently holding down one of these keys. (I have looked into msvcrt
and the like but have found no answer..) The function should also work
in both windows and Linux.

Any help is appriciated

You should have a look at the wxPython demo (wxKeyEvents section) that shows
how this is handled in a cross platform fashion.

Search for wxPython from www.sf.net

 

[Jarek Zgoda]

It's important to notice here that I'm not interested if the user has
already pressed shift or ctrl. I'm only interested in knowing if he is
currently holding down one of these keys. (I have looked into msvcrt
and the like but have found no answer..) The function should also work
in both windows and Linux.

This event *is* available in WinAPI, but don't ask me where. I'm sure,
because VCL (which is built on top of WinAPI and uses standard Windows
messages) distinguishes KeyUp and KeyDown events.

If you want to have it available also in linux, use Qt/PyQt.

 

[Jeff Epler]

In Tk, each event has a 'state' field, which can tell you whether
modifier keys or mouse buttons were pressed when an event was received.
Note that for the KeyPress event which is a modifier key, the state
field will not reflect the newly pressed key (the same goes for button
presses), as implied by this section of the XKeyEvent manpage:

The state member is set to indicate the logical state of the pointer
buttons and modifier keys just prior to the event, which is the bitwise
inclusive OR of one or more of the button or modifier key masks: But-
ton1Mask, Button2Mask, Button3Mask, Button4Mask, Button5Mask, Shift-
Mask, LockMask, ControlMask, Mod1Mask, Mod2Mask, Mod3Mask, Mod4Mask,
and Mod5Mask.

from Tkinter import *

# for pre-2.3 versions
#def enumerate(l):
# for i in range(len(l)): yield i, l

# Set up a mapping from bits to names
# (I'm not sure if these values match on Windows)
names = "Shift Caps Control Alt Num Mod3 Mod4 Mod5 1 2 3 4 5".split()
mods = [(1<<i, v) for i, v in enumerate(names)]

# Here's a handler that gets various events and looks at the state field
def setModifiers(event):
s = []
for i, v in mods:
if event.state & i: s.append(v)
if not s: s = ['(none)']
var.set(" ".join(s))

# Set up a minimal user interface
t = Tk()
var = StringVar(t)
l = Label(t, textv = var, width=32)
l.pack()

# including a couple of bindings (the text will update when
# one of these bindings is triggered)
for binding in "<Motion> <1> <ButtonRelease-1>".split():
l.bind(binding, setModifiers)
t.mainloop()

Jeff

 

[Thomas Heller]

Hey

I'm trying to build a gui application and need to know if the user is
actually holding down the shift or ctrl key. That is, if the user
currently is holding down the shift key. In pseudo code this will boil
down to something like this:

def test:
if user presses shift:
return SHIFT_IS_PRESSED
elif user presses ctrl:
return CTRL_IS_PRESSED
else
return false

It's important to notice here that I'm not interested if the user has
already pressed shift or ctrl. I'm only interested in knowing if he is
currently holding down one of these keys. (I have looked into msvcrt
and the like but have found no answer..) The function should also work
in both windows and Linux.

No idea about linux, but on windows you use win32api.GetKeyState().

Thomas

 

[Sean Richards]

Hey

I'm trying to build a gui application and need to know if the user is
actually holding down the shift or ctrl key. That is, if the user
currently is holding down the shift key. In pseudo code this will boil
down to something like this:

def test:
if user presses shift:
return SHIFT_IS_PRESSED
elif user presses ctrl:
return CTRL_IS_PRESSED
else
return false

It's important to notice here that I'm not interested if the user has
already pressed shift or ctrl. I'm only interested in knowing if he is
currently holding down one of these keys. (I have looked into msvcrt
and the like but have found no answer..) The function should also work
in both windows and Linux.

Any help is appriciated

In wxPython you could do it like this ...

1. Bind the key press events to the two functions

EVT_KEY_DOWN(self, self.OnKeyDown)
EVT_KEY_UP(self, self.OnKeyUp)

2. Set or unset a flag on keydown and keyup

def OnKeyDown(self, event):
if (event.GetKeyCode() == WXK_SHIFT):
self.Shift = True
elif (event.GetKeyCode() == WXK_CONTROL):
self.Control = True

def OnKeyUp(self, event):
if (event.GetKeyCode() == WXK_SHIFT):
self.Shift = False
elif (event.GetKeyCode() == WXK_CONTROL):
self.Control = False

Vennlig hilsen, Sean

 

[Richie Hindle]

[Rune]

It's important to notice here that I'm not interested if the user has
already pressed shift or ctrl. I'm only interested in knowing if he is
currently holding down one of these keys.
[Thomas]
No idea about linux, but on windows you use win32api.GetKeyState().

You mean GetAsyncKeyState: "The GetAsyncKeyState function determines
whether a key is up or down at the time the function is called"

Not GetKeyState: "The key status returned from this function changes as a
thread reads key messages from its message queue. The status does not
reflect the interrupt-level state associated with the hardware."

....assuming, Rune, that you *really do* want the current state. If your
program is event driven, and you're responding to Shift+Click or Ctrl+Drag
or similar, then you want GetKeyState. Imagine the machine is running
very slowly. I Shift+Click your app and release the Shift key before your
app responds. You call GetAsyncKeyState and see that Shift is not
pressed. Had you used GetKeyState, it would tell you that the Shift key
was pressed at the time of the click.