How to scroll text in Python/Curses subwindow?

Question

In my Python script which uses Curses, I have a subwin to which some text is assigned. Because the text length may be longer than the window size, the text should be scrollable.

Answer 1

Right, I was a bit confused on how to utilize pads (in order to scroll text), and still couldn't figure it out after reading this post; especially since I wanted to use it in a context of the content being an existing "array of lines". So I prepared a small example, that shows similarities (and differences) between newpad and subpad:

#!/usr/bin/env python2.7
import curses

# content - array of lines (list)
mylines = ["Line {0} ".format(id)*3 for id in range(1,11)]

import pprint
pprint.pprint(mylines)

def main(stdscr):
  hlines = begin_y = begin_x = 5 ; wcols = 10
  # calculate total content size
  padhlines = len(mylines)
  padwcols = 0
  for line in mylines:
    if len(line) > padwcols: padwcols = len(line)
  padhlines += 2 ; padwcols += 2 # allow border
  stdscr.addstr("padhlines "+str(padhlines)+" padwcols "+str(padwcols)+"; ")
  # both newpad and subpad are :
  mypadn = curses.newpad(padhlines, padwcols)
  mypads = stdscr.subpad(padhlines, padwcols, begin_y, begin_x+padwcols+4)
  stdscr.addstr(str(type(mypadn))+" "+str(type(mypads)) + "\n")
  mypadn.scrollok(1)
  mypadn.idlok(1)
  mypads.scrollok(1)
  mypads.idlok(1)
  mypadn.border(0) # first ...
  mypads.border(0) # ... border
  for line in mylines:
    mypadn.addstr(padhlines-1,1, line)
    mypadn.scroll(1)
    mypads.addstr(padhlines-1,1, line)
    mypads.scroll(1)
  mypadn.border(0) # second ...
  mypads.border(0) # ... border
  # refresh parent first, to render the texts on top
  #~ stdscr.refresh()
  # refresh the pads next
  mypadn.refresh(0,0, begin_y,begin_x, begin_y+hlines, begin_x+padwcols)
  mypads.refresh()
  mypads.touchwin()
  mypadn.touchwin()
  stdscr.touchwin() # no real effect here
  #stdscr.refresh() # not here! overwrites newpad!
  mypadn.getch()
  # even THIS command erases newpad!
  # (unless stdscr.refresh() previously):
  stdscr.getch()

curses.wrapper(main)

When you run this, at first you will get something like (newpad left, subpad right):

 ┌────────────────────────┐    ┌────────────────────────┐
 │Line 1 Line 1 Line 1 ───│    │Line 1 Line 1 Line 1 ───│
 │Line 2 Line 2 Line 2    │    │Line 2 Line 2 Line 2    │
 │Line 3 Line 3 Line 3    │    │Line 3 Line 3 Line 3    │
 │Line 4 Line 4 Line 4    │    │Line 4 Line 4 Line 4    │
 │Line 5 Line 5 Line 5    │    │Line 5 Line 5 Line 5    │
                               │Line 6 Line 6 Line 6    │
                               │Line 7 Line 7 Line 7    │
                               │Line 8 Line 8 Line 8    │
                               │Line 9 Line 9 Line 9    │
                               │Line 10 Line 10 Line 10 │
                               └────────────────────────┘

Some notes:

• Both newpad and subpad should have their width/height sized to the content (num lines/max line width of the array of lines) + eventual border space
• In both cases, you could allow extra lines with scrollok() - but not extra width
• In both cases, you basically "push" a line at the bottom of the pad; and then scroll() up to make room for the next
• The special refresh method that newpad has, then allows for just a region of this "whole content" to be shown on screen; subpad more-less has to be shown in the size it was instantiated in
• If you draw the borders of the pads before adding content strings - then the borders will scroll up too (that is the ─── piece shown at the ...Line 1 ───│ part).

Useful links:

• (n)curses pad in python not working
• http://threeseas.net/vic/vic/terminal.py
• How do I delete a curse window in python and restore background window?