Python program to take user input and refresh console without "scrolling"

Question

Let's say I have this little Python program:

def drawLine():

    userInput = input("Coordinates:")
    userInput = userInput.split() # x y

    # Draw
    # ... some drawing algo which will print an "X" on the screen with x,y

drawLine()
drawLine()

Now notice that drawLine() is called twice, so that two inputs can be taken and two X-es be drawn. Unfortunately, console will scroll up. I want my python program "to listen" to user key presses and "not scroll away". Think of a mini-console Photoshop, which also does not scroll your canvas out of sight.

Update: Problem is small enough to not employ a library.

If you don't want to use a library you will be writing a lot of fiddly code. Use a library. — Ethan Furman, Mar 21 '16 at 23:09
At the very least, check out the code the libraries use to get an idea of how it's done. — Ethan Furman, Mar 21 '16 at 23:10
Checking libraries is a great idea. I figure this problem was already solved somewhere else. Mabye somebody knows without me spending couple of minutes or even hours with Google. — Stephan Kristyn, Mar 21 '16 at 23:11

Łukasz Lalik · Answer 1 · 2016-03-21T23:08:48.013

1

Probably Curses library is what you need in this case.

It allows you to display string at given coordinates: https://docs.python.org/3.3/library/curses.html#curses.window.addstr

You can also leave echo mode so you can handle keyboard input as you want without printing it to console: https://docs.python.org/3.3/library/curses.html#curses.noecho.

edited Mar 21 '16 at 23:08

answered Mar 21 '16 at 23:08

Łukasz Lalik

61
5

No Libraries! Sorry. – Stephan Kristyn Mar 21 '16 at 23:08

score 1 · Answer 2 · edited May 23 '17 at 12:03

1

I'm not sure if I fully understand your question but I think it can be achieve by clearing console and redrawing the 'frame'. How to clear the interpreter console?

edited May 23 '17 at 12:03

Community

1
1

answered Mar 21 '16 at 23:08

W33P

11
3

score 1 · Accepted Answer · answered Mar 21 '16 at 23:26

1

Using VT100 control codes:

input("something:")
print( '\x1b[1A\x1b[2K\x1b[1A')
input("something else:")

There must be something similar for windows.

answered Mar 21 '16 at 23:26

xvan

4,554
1
22
37

Thanks @xvan, these work great for my purposes - http://www.ccs.neu.edu/research/gpc/MSim/vona/terminal/VT100_Escape_Codes.html – Stephan Kristyn Mar 21 '16 at 23:34

score 1 · Answer 4 · edited May 23 '17 at 10:33

If it was alright to keep the input below the console, you could use a class to keep your canvas in an array and just render it when you need to.

Here is an example:

#X-Drawer
class Canvas:
    def __init__(self, w, h):
        self.w = w
        self.h = h
        self.c = []
        for i in range(w * h):
            self.c.append(' ')
        print len(self.c)
    def render(self):
        u = 0
        s = ""
        for i in range(len(self.c)):
            s += self.c[i]
            if not i % self.w:
                s += "\n"
        print s
    def drawX(self, x, y):
        n = [(x, y), (x + 1, y + 1), (x + 2, y + 2), (x + 2, y), (x, y + 2)]
        for i in n:
            v = i[0] * self.w + i[1]
            if v < len(self.c):
                self.c[v] = 'X'
    def drawLine(self, x, d):
        n = []
        if d:
            n = [(x, y), (x + 1, y + 1), (x + 2, y + 2)]
        else:
            n = [(x, y), (x + 1, y + 1), (x + 2, y + 2)]
        for i in n:
            v = i[0] * self.w + i[1]
            if v < len(self.c):
                self.c[v] = 'X'

def clearScreen():
    for i in range(64):
        print

c = Canvas(25, 25)

while True:
    clearScreen()
    c.render()
    i = raw_input("Coordinates: ").split()
    c.drawX(int(i[0]), int(i[1]))

You could also replace the clearScreen with an os call to clr ( How to clear the interpreter console? ) instead of printing 64 lines.

Note: My example uses the drawX function, you could use the drawLine function and different coordinates to draw the lines.

Python program to take user input and refresh console without "scrolling"

4 Answers4