Draw a square in the screen, move it with arrow keys -- experimenting with urwid

square.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""Draw a square in the screen, move it with arrow keys
"""

from __future__ import print_function, absolute_import, division
import urwid


BLOCK = u"""
╭───╮
│   │
╰───╯
""".strip()

BOX_ROWS = len(BLOCK.splitlines())
BOX_COLS = len(BLOCK.splitlines()[0])


def exit_on_q_or_esc(key):
    if key in ('esc', 'q', 'Q'):
        raise urwid.ExitMainLoop()


class MoveableBox(urwid.WidgetWrap):
    def selectable(self):
        return True

    def __init__(self):
        self._padding_left = 0
        self._padding_top = 0
        self.text = urwid.Text(BLOCK)
        self.container = self._build_widget()
        self.pile = urwid.Pile([])
        self.redraw()
        super(MoveableBox, self).__init__(self.pile)

    @property
    def padding_left(self):
        return self._padding_left

    @padding_left.setter
    def padding_left(self, value):
        self._padding_left = value if value > 0 else 0

    @property
    def padding_top(self):
        return self._padding_top

    @padding_top.setter
    def padding_top(self, value):
        self._padding_top = value if value > 0 else 0

    def _build_widget(self):
        filler = urwid.Filler(self.text, 'top', top=self.padding_top)
        return urwid.Padding(filler, left=self.padding_left)

    def redraw(self):
        self.pile.contents[:] = [(self._build_widget(), self.pile.options())]

    def keypress(self, size, key):
        maxcol, maxrow = size
        h_increment = 2
        v_increment = 1
        if key in ('right'):
            if maxcol > self.padding_left + BOX_COLS + h_increment:
                self.padding_left += h_increment
                self.redraw()
        elif key in ('left'):
            self.padding_left -= h_increment
            self.redraw()
        elif key in ('up'):
            self.padding_top -= v_increment
            self.redraw()
        elif key in ('down'):
            if maxrow > self.padding_top + BOX_ROWS:
                self.padding_top += v_increment
                self.redraw()
        else:
            return super(MoveableBox, self).keypress(size, key)


def run(args):
    box = MoveableBox()
    loop = urwid.MainLoop(box, unhandled_input=exit_on_q_or_esc)
    loop.run()


if '__main__' == __name__:
    import argparse
    parser = argparse.ArgumentParser(description=__doc__)

    args = parser.parse_args()
    run(args)