getch() in Python

[nutshelluniverse]

Is there a function that waits for a keypress before continuing in Python 3.2?

I'm looking for something similar to getch() in C or GET/GET$ in BBC BASIC

[DougieLawson]

Code: Select all

#!/usr/bin/python

import sys, tty, termios

fd = sys.stdin.fileno()
old_settings = termios.tcgetattr(fd)
tty.setraw(sys.stdin.fileno())

ch = sys.stdin.read(1)

termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
print '\nchar is\'' + ch + '\'\n'

[nutshelluniverse]

Code: Select all

#!/usr/bin/python

import sys, tty, termios

fd = sys.stdin.fileno()
old_settings = termios.tcgetattr(fd)
tty.setraw(sys.stdin.fileno())

ch = sys.stdin.read(1)

termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
print '\nchar is\'' + ch + '\'\n'

Although that does work on Python 2.7, what's the 3.2 equivalent?

[DougieLawson]

Although that does work on Python 2.7, what's the 3.2 equivalent?

Sorry, I don't know. I've no desire to move to python3 because too many python2 things are incompatible and most of the free code and code samples out on the Internet is python2.

[jojopi]

Python 3 just needs parentheses on the print.

Unless you really need to read control Ctrl+C as a normal character (which makes interrupting the program difficult) it is safer to disable canonical input, rather than setting full raw mode. Also it is good practice to try to restore the terminal settings if something goes wrong.

Code: Select all

def getch():
  import sys, tty, termios
  old_settings = termios.tcgetattr(0)
  new_settings = old_settings[:]
  new_settings[3] &= ~termios.ICANON
  try:
    termios.tcsetattr(0, termios.TCSANOW, new_settings)
    ch = sys.stdin.read(1)
  finally:
    termios.tcsetattr(0, termios.TCSANOW, old_settings)
  return ch

print("\nchar is '" + getch() + "'\n")

[nutshelluniverse]

Python 3 just needs parentheses on the print.

Unless you really need to read control Ctrl+C as a normal character (which makes interrupting the program difficult) it is safer to disable canonical input, rather than setting full raw mode. Also it is good practice to try to restore the terminal settings if something goes wrong.

Code: Select all

def getch():
  import sys, tty, termios
  old_settings = termios.tcgetattr(0)
  new_settings = old_settings[:]
  new_settings[3] &= ~termios.ICANON
  try:
    termios.tcsetattr(0, termios.TCSANOW, new_settings)
    ch = sys.stdin.read(1)
  finally:
    termios.tcsetattr(0, termios.TCSANOW, old_settings)
  return ch

print("\nchar is '" + getch() + "'\n")

Oh right.

[keybeeper]

Anyone learning Python should be encouraged to use Python3. The differences are few and Python3 clears up some of the inconsistencies in Python2. As mentioned by jojopi the main difference you will come across is the print statement. If you are copying Python2 code just put the arguments in parentheses.

Python2 is of the past, Python3 is now and the future.


Simple guide here:

http://www.cs.carleton.edu/faculty/jgol ... on2vs3.pdf


for a getch() function look here:

https://pypi.python.org/pypi/getch

[stevech]

Opinion: For all but very advanced users, I'd avoid all things Python 3 and stay in the Python 2 world.

[keybeeper]

Why stay with Python2? Why is it only for very advanced users? I'm a new user and have had no difficulty whatever with Python3. It's virtually the same. In fact I have copied example code written in Python2 into Python3 programs and didn't realise that it was written in Python2. The code worked OK. I prefer to look to the future, not get stuck in the past.

[paddyg]

Even until 6 months ago there were quite important modules that were available for python2 but hadn't yet been converted to work with python3 (and a similar situation applies to pypy) However I think most important things now work in python3 and there are many new modules that won't work in python2, but it takes a while for the world to migrate. For instance the python-imaging library stopped being maintained ages ago, before python3 was sorted so it you wanted to use it for image processing you had to stick to python2. However the Pillow fork of PIL has kept bug fixing and improving the module so it must be better, and it works on python3 and pypy. However on raspbian the decrepit PIL is still automatically included as the graphics module for python, and if you want to apt-get install it you need to point to the 'jessie' repository. (On Arch, interestingly python == python3 and you have to specify python2 if you want that. And you can just pacman -S python-pillow, and Ubuntu is starting to include pillow rather than PIL now I think)

[nutshelluniverse]

So where does the getch() function fit into this?

[paddyg]

I user curses getch() which seems to work fine with p2 or p3 (is unhappy when run under idle)

[keybeeper]

As suggested in my previous reply, did you remember to look here?

https://pypi.python.org/pypi/getch

[Uhgtred]

Anyone learning Python should be encouraged to use Python3. The differences are few and Python3 clears up some of the inconsistencies in Python2. As mentioned by jojopi the main difference you will come across is the print statement. If you are copying Python2 code just put the arguments in parentheses.

Python2 is of the past, Python3 is now and the future.


Simple guide here:

http://www.cs.carleton.edu/faculty/jgol ... on2vs3.pdf


for a getch() function look here:

https://pypi.python.org/pypi/getch

what exactly does this return when no key is pressed? i want to abort a programm when no key is pressed and want it running as long as the key is pressed.

[paddyg]

I think the getch() as used in C will not return until it gets a key press. i.e. it will block the program execution. You could use the curses version I linked to and set the timeout to 0 i.e. like we do here. Or you could do the key press checking in another thread with a loop to set the time a key was pressed. If the time was more than a certain value you could quit. Something along the lines of this completely untested code.

Code: Select all

import time, threading, getch
..
key = 'start'
tm = 0.0
running = True

def check_keys():
  global key, tm, running
  while running:
    key = getch()
    tm = time.time()

t = threading.Thread(target=check_keys)
t.start()

while running:
  ...
  # do whatever you program does
  if tm - time.time() > 0.5 and key != 'start':
    # button not being pressed fast enough
    running = False