I want my script to wait until the user presses any key.
How do I do that?
This question is related to
python
wait
keyboard-input
One way to do this in Python 2, is to use raw_input():
raw_input("Press Enter to continue...")
In python3 it's just input()
os.system seems to always invoke sh, which does not recognize the s and n options for read. However the read command can be passed to bash:
os.system("""bash -c 'read -s -n 1 -p "Press any key to continue..."'""")
On my linux box, I use the following code. This is similar to code I've seen elsewhere (in the old python FAQs for instance) but that code spins in a tight loop where this code doesn't and there are lots of odd corner cases that code doesn't account for that this code does.
def read_single_keypress():
"""Waits for a single keypress on stdin.
This is a silly function to call if you need to do it a lot because it has
to store stdin's current setup, setup stdin for reading single keystrokes
then read the single keystroke then revert stdin back after reading the
keystroke.
Returns a tuple of characters of the key that was pressed - on Linux,
pressing keys like up arrow results in a sequence of characters. Returns
('\x03',) on KeyboardInterrupt which can happen when a signal gets
handled.
"""
import termios, fcntl, sys, os
fd = sys.stdin.fileno()
# save old state
flags_save = fcntl.fcntl(fd, fcntl.F_GETFL)
attrs_save = termios.tcgetattr(fd)
# make raw - the way to do this comes from the termios(3) man page.
attrs = list(attrs_save) # copy the stored version to update
# iflag
attrs[0] &= ~(termios.IGNBRK | termios.BRKINT | termios.PARMRK
| termios.ISTRIP | termios.INLCR | termios. IGNCR
| termios.ICRNL | termios.IXON )
# oflag
attrs[1] &= ~termios.OPOST
# cflag
attrs[2] &= ~(termios.CSIZE | termios. PARENB)
attrs[2] |= termios.CS8
# lflag
attrs[3] &= ~(termios.ECHONL | termios.ECHO | termios.ICANON
| termios.ISIG | termios.IEXTEN)
termios.tcsetattr(fd, termios.TCSANOW, attrs)
# turn off non-blocking
fcntl.fcntl(fd, fcntl.F_SETFL, flags_save & ~os.O_NONBLOCK)
# read a single keystroke
ret = []
try:
ret.append(sys.stdin.read(1)) # returns a single character
fcntl.fcntl(fd, fcntl.F_SETFL, flags_save | os.O_NONBLOCK)
c = sys.stdin.read(1) # returns a single character
while len(c) > 0:
ret.append(c)
c = sys.stdin.read(1)
except KeyboardInterrupt:
ret.append('\x03')
finally:
# restore old state
termios.tcsetattr(fd, termios.TCSAFLUSH, attrs_save)
fcntl.fcntl(fd, fcntl.F_SETFL, flags_save)
return tuple(ret)
The python manual provides the following:
import termios, fcntl, sys, os
fd = sys.stdin.fileno()
oldterm = termios.tcgetattr(fd)
newattr = termios.tcgetattr(fd)
newattr[3] = newattr[3] & ~termios.ICANON & ~termios.ECHO
termios.tcsetattr(fd, termios.TCSANOW, newattr)
oldflags = fcntl.fcntl(fd, fcntl.F_GETFL)
fcntl.fcntl(fd, fcntl.F_SETFL, oldflags | os.O_NONBLOCK)
try:
while 1:
try:
c = sys.stdin.read(1)
print "Got character", repr(c)
except IOError: pass
finally:
termios.tcsetattr(fd, termios.TCSAFLUSH, oldterm)
fcntl.fcntl(fd, fcntl.F_SETFL, oldflags)
which can be rolled into your use case.
Simply using
input("Press Enter to continue...")
will cause a SyntaxError: expected EOF while parsing.
Simple fix use:
try:
input("Press enter to continue")
except SyntaxError:
pass
I don't know of a platform independent way of doing it, but under Windows, if you use the msvcrt module, you can use its getch function:
import msvcrt
c = msvcrt.getch()
print 'you entered', c
mscvcrt also includes the non-blocking kbhit() function to see if a key was pressed without waiting (not sure if there's a corresponding curses function). Under UNIX, there is the curses package, but not sure if you can use it without using it for all of the screen output. This code works under UNIX:
import curses
stdscr = curses.initscr()
c = stdscr.getch()
print 'you entered', chr(c)
curses.endwin()
Note that curses.getch() returns the ordinal of the key pressed so to make it have the same output I had to cast it.
I am new to python and I was already thinking I am too stupid to reproduce the simplest suggestions made here. It turns out, there's a pitfall one should know:
When a python-script is executed from IDLE, some IO-commands seem to behave completely different (as there is actually no terminal window).
Eg. msvcrt.getch is non-blocking and always returns $ff. This has already been reported long ago (see e.g. https://bugs.python.org/issue9290 ) - and it's marked as fixed, somehow the problem seems to persist in current versions of python/IDLE.
So if any of the code posted above doesn't work for you, try running the script manually, and NOT from IDLE.
If you are ok with depending on system commands you can use the following:
Linux and Mac OS X:
import os
os.system('read -s -n 1 -p "Press any key to continue..."')
print()
Windows:
import os
os.system("pause")
If you want to see if they pressed a exact key (like say 'b') Do this:
while True:
choice = raw_input("> ")
if choice == 'b' :
print "You win"
input("yay")
break
If you want to wait for enter (so the user knocking the keyboard does not cause something un-intended to happen) use
sys.stdin.readline()
Cross Platform, Python 2/3 code:
# import sys, os
def wait_key():
''' Wait for a key press on the console and return it. '''
result = None
if os.name == 'nt':
import msvcrt
result = msvcrt.getch()
else:
import termios
fd = sys.stdin.fileno()
oldterm = termios.tcgetattr(fd)
newattr = termios.tcgetattr(fd)
newattr[3] = newattr[3] & ~termios.ICANON & ~termios.ECHO
termios.tcsetattr(fd, termios.TCSANOW, newattr)
try:
result = sys.stdin.read(1)
except IOError:
pass
finally:
termios.tcsetattr(fd, termios.TCSAFLUSH, oldterm)
return result
I removed the fctl/non-blocking stuff because it was giving IOErrors and I didn't need it. I'm using this code specifically because I want it to block. ;)
Addendum:
I implemented this in a package on PyPI with a lot of other goodies called console:
>>> from console.utils import wait_key
>>> wait_key()
'h'
Source: Stackoverflow.com