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@ajaygunalan
Last active Mar 29, 2019
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Non-Block Communication in Python
from non_blocking import *
def HigherControl(k, v0):
if k == 'w':
v = v0 + 0.001
elif k == 's':
v = v0 - 0.001
else:
v = v0
if k == 'a':
omega = 0.25
elif k == 'd':
omega = -0.25
else:
omega = 0
return [v, omega]
global v0
v0 = 0.0
# def a(val):
# # print val
# global initial
# initial = val + 1
# print initial
def get_input(k):
global v0
[v0, omega] = HigherControl(k, v0)
print ("V, w")
print ([v0, omega])
kb = KBHit()
while True:
if kb.kbhit():
c = kb.getch()
if ord(c) == 27: # ESC
break
get_input(c)
kb.set_normal_term()
#include <fstream>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <stdio.h>
#include <string>
#include <ncurses.h>
#include <unistd.h>
#define SLEEP( milliseconds ) usleep( (unsigned long) (milliseconds * 1000.0) )
int main()
{
int ch;
initscr(); /* Start curses mode */
raw(); /* Line buffering disabled */
keypad(stdscr, TRUE); /* We get F1, F2 etc.. */
noecho(); /* Don't echo() while we do getch */
while (1)
{
SLEEP( 100 );
printw("Exit: Esc key\n");
ch = getch(); /* If raw() hadn't been called
* we have to press enter before it
* gets to the program */
if(ch == 27) // Esc key
{
endwin(); /* End curses mode */
exit(0);
//return 0;
}
else
{ printw("The pressed key is ");
attron(A_BOLD);
printw("%c\n", ch);
attroff(A_BOLD);
}
//refresh(); /* Print it on to the real screen */
//getch(); /* Wait for user input */
}
endwin(); /* End curses mode */
exit(1);
//return 0;
}
/**How to Compile and Run **/
g++ FILE_NAME.cpp -lncurses -o EXECUTABLE_NAME
./EXECUTABLE_NAME
#!/usr/bin/env python
'''
A Python class implementing KBHIT, the standard keyboard-interrupt poller.
Works transparently on Windows and Posix (Linux, Mac OS X). Doesn't work
with IDLE.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
'''
import os
# Windows
if os.name == 'nt':
import msvcrt
# Posix (Linux, OS X)
else:
import sys
import termios
import atexit
from select import select
class KBHit:
def __init__(self):
'''Creates a KBHit object that you can call to do various keyboard things.
'''
if os.name == 'nt':
pass
else:
# Save the terminal settings
self.fd = sys.stdin.fileno()
self.new_term = termios.tcgetattr(self.fd)
self.old_term = termios.tcgetattr(self.fd)
# New terminal setting unbuffered
self.new_term[3] = (self.new_term[3] & ~termios.ICANON & ~termios.ECHO)
termios.tcsetattr(self.fd, termios.TCSAFLUSH, self.new_term)
# Support normal-terminal reset at exit
atexit.register(self.set_normal_term)
def set_normal_term(self):
''' Resets to normal terminal. On Windows this is a no-op.
'''
if os.name == 'nt':
pass
else:
termios.tcsetattr(self.fd, termios.TCSAFLUSH, self.old_term)
def getch(self):
''' Returns a keyboard character after kbhit() has been called.
Should not be called in the same program as getarrow().
'''
s = ''
if os.name == 'nt':
return msvcrt.getch().decode('utf-8')
else:
return sys.stdin.read(1)
def getarrow(self):
''' Returns an arrow-key code after kbhit() has been called. Codes are
0 : up
1 : right
2 : down
3 : left
Should not be called in the same program as getch().
'''
if os.name == 'nt':
msvcrt.getch() # skip 0xE0
c = msvcrt.getch()
vals = [72, 77, 80, 75]
else:
c = sys.stdin.read(3)[2]
vals = [65, 67, 66, 68]
return vals.index(ord(c.decode('utf-8')))
def kbhit(self):
''' Returns True if keyboard character was hit, False otherwise.
'''
if os.name == 'nt':
return msvcrt.kbhit()
else:
dr,dw,de = select([sys.stdin], [], [], 0)
return dr != []
# Test
if __name__ == "__main__":
kb = KBHit()
print('Hit any key, or ESC to exit')
while True:
if kb.kbhit():
c = kb.getch()
if ord(c) == 27: # ESC
break
print(c)
kb.set_normal_term()
@ajaygunalan

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@ajaygunalan ajaygunalan commented Nov 27, 2018

Non-Block Communication in Python

In python, if you want to have user input, you can use input or raw_input but the problem is the entire script waits for the input till timeout occurs. This is known as Blocking I/O.

We wanted to control the stoch robot like playing a video game. i.e., we wanted the script to run irrespective of the user input. The solution is to use the non-blokcing I/O. It can implemented via either Threading or Select.

Clone it and run python controller.py or python3 controller.py

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