There are at least two ways to approach this.

The first is to check whether your "standard input" stream has some data, without blocking to actually wait till there is some. The answers referenced in comments tell you how to approach this. However, while this is attractive in terms of simplicity (compared to the alternatives), there is no way to transparently do this portably between Windows and Linux.

The second way is to use a thread to block and wait for the user input:

import threading 
import time

no_input = True

def add_up_time():
    print "adding up time..."
    timeTaken=float(0)
    while no_input:
        time.sleep(0.01)
        timeTaken=timeTaken+0.01
    print(timeTaken)


# designed to be called as a thread
def signal_user_input():
    global no_input
    i = raw_input("hit enter to stop things")   # I have python 2.7, not 3.x
    no_input = False
    # thread exits here


# we're just going to wait for user input while adding up time once...
threading.Thread(target = signal_user_input).start()

add_up_time()

print("done.... we could set no_input back to True and loop back to the previous comment...")

As you can see, there's a bit of a dilemma about how to communicate from the thread to the main loop that the input has been received. Global variable to signal it... yucko eh?

In Python 3, use input():

input("Press Enter to continue...")

In Python 2, use raw_input():

raw_input("Press Enter to continue...")

This only waits for the user to press enter though.

On Windows/DOS, one might want to use msvcrt. The msvcrt module gives you access to a number of functions in the Microsoft Visual C/C++ Runtime Library (MSVCRT):

import msvcrt as m
def wait():
    m.getch()

This should wait for a key press.

Notes:

In Python 3, raw_input() does not exist.
In Python 2, input(prompt) is equivalent to eval(raw_input(prompt)).

The best thing to do in this case is to use some sort of UI library that contains an event loop. You poll this event loop for things that happen including keys pressed and mouse clicks.

If you want to do this in a terminal, there is Urwid. If you want to do it as a GUI there are tons of systems available, like:

• Gnome
• GTK
• KDE
• Tcl/Tk
• Qt4
• Kivy

And more of them, and then loads more which aren't cross-platform.

Actually in the meantime (almost 10 years from the start of this thread) a cross-platform module named pynput appeared. Below a first cut - i.e. that works with lowercase 's' only. I have tested it on Windows but I am almost 100% positive that it should work on Linux.

from pynput import keyboard

print('Press s or n to continue:')

with keyboard.Events() as events:
    # Block for as much as possible
    event = events.get(1e6)
    if event.key == keyboard.KeyCode.from_char('s'):
        print("YES")

I'm posting this answer for a subtle variation of this issue that I encountered, where the Python console would not let me enter my input but unlike in your case, would not move on with the loop.

I solved the problem by clicking on "Edit the configurations" on the toolbar (run/debug configurations) and disabling the option "Emulate terminal in output console".

Hopefully those having the same issue will stumble upon this thread (as I did).

EDIT: In images:

I haven't tried that solution with a remote interpreter.

Have a look at official document about coroutines.

Example:

import time, asyncio

async def run_task():
    for i in range(5):
        print('running task %d' % i)
        await awaiting_task(i)

async def awaiting_task(name):
    time.sleep(5) # wait for 5 seconds
    print('task %s finished' % str(name))

asyncio.run(run_task())

The async syntax will turn the function to a coroutine, which saves your cpu if possible, other than busy waiting.