Log error when the espeak plugin is not installed.

Now when the espeak plugin is not installed there will be an
error (logging.error) in the log. Instead of the ugly message
of Gst
Also, if Gst isnt installed it debug a error too.

Fixes #3345

src/sugar3/speech.py

@@ -18,12 +18,18 @@ import os
 import logging
 from gettext import gettext as _
 
+from gi.repository.GLib import GError
 from gi.repository import Gio
-from gi.repository import Gst
 from gi.repository import Gtk
 from gi.repository import Gdk
 from gi.repository import GObject
 
+_HAS_GST = True
+try:
+    from gi.repository import Gst
+except:
+    _HAS_GST = False
+
 from sugar3 import power
 
 DEFAULT_PITCH = 0
@@ -110,6 +116,24 @@ translated_espeak_voices = {
 }
 
 
+def _has_espeak_module():
+    try:
+        Gst.parse_launch('espeak')
+    except GError:
+        logging.error('The speech plugin is not installed in the system.')
+        return False
+    return True
+
+
+def _check_modules():
+    if not _HAS_GST:
+        logging.error('GST is not installed in the system.')
+        return False
+    if not _has_espeak_module():
+        return False
+    return True
+
+
 class SpeechManager(GObject.GObject):
 
     __gtype_name__ = 'SpeechManager'
@@ -128,6 +152,10 @@ class SpeechManager(GObject.GObject):
 
     def __init__(self, **kwargs):
         GObject.GObject.__init__(self, **kwargs)
+        self._player = None
+        if not self.enabled():
+            return
+
         self._player = _GstSpeechPlayer()
         self._player.connect('play', self._update_state, 'play')
         self._player.connect('stop', self._update_state, 'stop')
@@ -140,6 +168,9 @@ class SpeechManager(GObject.GObject):
         self._save_timeout_id = -1
         self.restore()
 
+    def enabled(self):
+        return _check_modules()
+
     def _update_state(self, player, signal):
         self._is_playing = (signal == 'play')
         self._is_paused = (signal == 'pause')
@@ -227,10 +258,14 @@ class SpeechManager(GObject.GObject):
                       self._pitch, self._rate)
 
     def get_all_voices(self):
-        return self._player.get_all_voices()
+        if self._player:
+            return self._player.get_all_voices()
+        return None
 
     def get_all_traslated_voices(self):
-        return self._player.get_all_translated_voices()
+        if self._player:
+            return self._player.get_all_voices()
+        return None
 
 
 class _GstSpeechPlayer(GObject.GObject):