python 2.7.12 on Linux behaving differently than on Windows
bc at freeuk.com
Thu Dec 8 07:43:18 EST 2016
On 08/12/2016 07:24, Gregory Ewing wrote:
> BartC wrote:
>> (I'm in the middle of porting my console editor to Linux. But one
>> problem is that on one Linux, half the key combinations (eg.
>> Shift+Ctrl+B) are not recognised.
> If you're reading characters from a tty device in raw
> mode (which I assume is what you mean by "console editor")
> I'm not aware of *any* Unix system that will let you
> distinguish between Ctrl+B and Shift+Ctrl+B that way.
> That's because the tty driver delivers ASCII characters,
> and there are no separate ASCII codes for shifted control
Run the code below and start pressing keys. On both of my Linuxes, I get
escape sequences shown when I Insert, Delete, Home, End, Page Up, Page
Down, Up, Down, Left, Right and most of the function keys; not just
single ASCII codes.
But I also get different sequences, on Ubuntu, when I press Shift, Ctrl
or Alt with those keys, but not all shifts nor combinations will work
(some have special meanings anyway).
Then I try the same on Debian (I think it is) on a Raspberry Pi, and
most Shift and Ctrl are ignored, except for Ctrl A to Z (with a few gaps).
(Neither will see Shift+Ctrl+B, which means go to start of the file,
same as Ctrl+Home. Ubuntu sees Ctrl+Home, but not Debian, although it
will report Alt+Home. And some laptop keyboards already have Home on an
Alternate-Function shift! It's a mess.)
>> Except that was only two Linuxes; perhaps on others, the keyboard will
>> likely be crippled in some other way.
> No, they'll all be the same -- if it has an ASCII code,
> you'll be able to get it from a tty device, otherwise you
>> How people manage to do anything on such an OS I've no idea.
> Programs that need to be able to distinguish all of the
> modifiers are normally implemented as GUI applications,
> which get keyboard input a different way.
How do they work; what magic do they use to get that key information,
and why can't it be done outside of a GUI? As I understand a Linux GUI
is built on top of Linux.
# Python 2 because of the 'print' handling
def getch(): # adapted from first getch I saw on the internet
import sys, tty, termios
fd = sys.stdin.fileno()
old_settings = termios.tcgetattr(fd)
ch = sys.stdin.read(1)
termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
print "Press keys"
print ("Hit Escape twice to quit")
print "Esc ",
if escape: break
escape = k==27
(On another test, using a C-based getch(), pressing Enter returns code
10 not 13; another difference to note. Either code appears to clash with
Ctrl-M or Ctrl-J, a difference from Windows where Ctrl-J, Ctrl-M and
Enter are distinct keys, as they are in actuality.)
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