Fails with Ubuntu 18.04

[quozl]

Activity does not start. Logs contain;

(sugar-activity:1468): Gtk-WARNING **: 07:44:24.571: Locale not supported by C library.
        Using the fallback 'C' locale.
/home/olpc/Activities/Ruler.activity/RulerActivity.py:22: PyGIWarning: Gtk was imported without specifying a version first. Use gi.require_version('Gtk', '3.0') before import to ensure that the right version gets loaded.
  from gi.repository import Gtk
/home/olpc/Activities/Ruler.activity/util.py:32: PyGIWarning: PangoCairo was imported without specifying a version first. Use gi.require_version('PangoCairo', '1.0') before import to ensure that the right version gets loaded.
  from gi.repository import PangoCairo
/usr/bin/sugar-activity:48: Warning: g_hash_table_destroy: assertion 'hash_table != NULL' failed
  activity = constructor(handle)
python: ../../../../src/cairo-surface.c:2994: _cairo_surface_create_in_error: Assertion `status < CAIRO_STATUS_LAST_STATUS' failed.
Terminated by signal 6, pid 1468 data (<open file '<fdopen>', mode 'w' at 0x7fe038a9ef60>, '47b8e304b7cd61aef2812034187ee1f23c9e7e9c')

[quozl]

Occurs in the call to PangoCairo.create_layout while drawing the default ruler.

  File "/usr/bin/sugar-activity", line 219, in <module>
    main()
  File "/usr/bin/sugar-activity", line 217, in main
    instance.run_main_loop()
  File "/usr/lib/python2.7/sugar3/activity/activity.py", line 464, in run_main_loop
    Gtk.main()
  File "/usr/share/sugar/activities/Ruler.activity/RulerActivity.py", line 75, in __expose_event_cb
    self._object.draw(cr, self._dpi)
  File "/usr/share/sugar/activities/Ruler.activity/show_rulers.py", line 49, in draw
    self.draw_ruler_pair(c, dpi, mm(dpi, 20))
  File "/usr/share/sugar/activities/Ruler.activity/show_rulers.py", line 80, in draw_ruler_pair
    self.draw_cm_ruler(c, dpi)
  File "/usr/share/sugar/activities/Ruler.activity/show_rulers.py", line 160, in draw_cm_ruler
    write(c, "%d" % n, self.font_bold, mm(dpi, 2.5), centered=True)

[quozl]

On Ubuntu 20.04 the signal is replaced by a complete traceback;

Traceback (most recent call last):
  File "/usr/share/sugar/activities/Ruler.activity/RulerActivity.py", line 75, in __expose_event_cb
    self._object.draw(cr, self._dpi)
  File "/usr/share/sugar/activities/Ruler.activity/show_rulers.py", line 47, in draw
    self.draw_ruler_pair(c, dpi, mm(dpi, 20))
  File "/usr/share/sugar/activities/Ruler.activity/show_rulers.py", line 78, in draw_ruler_pair
    self.draw_cm_ruler(c, dpi)
  File "/usr/share/sugar/activities/Ruler.activity/show_rulers.py", line 158, in draw_cm_ruler
    write(c, "%d" % n, self.font_bold, mm(dpi, 2.5), centered=True)
  File "/usr/share/sugar/activities/Ruler.activity/util.py", line 107, in write
    lo = PangoCairo.create_layout(pc)
TypeError: Expected cairo.Context

[Saumya-Mishra9129]

I suggest testing with 2d3d3c0 once.It should fix this issue as well as #4.