-

 plover/steno_dictionary.py |  4 ++--
 plover/translation.py      | 10 +++++-----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git i/plover/steno_dictionary.py w/plover/steno_dictionary.py
index d9ddcce3..486dd932 100644
--- i/plover/steno_dictionary.py
+++ w/plover/steno_dictionary.py
@@ -66,7 +66,7 @@ class StenoDictionary(collections.MutableMapping):
                 self._longest_key = 0
 
     def __contains__(self, key):
-        return self.get(key) is not None
+        return key in self._dict
 
     def reverse_lookup(self, value):
         return self.reverse.get(value, ())
@@ -126,7 +126,7 @@ class StenoDictionaryCollection(object):
             if key_len > d.longest_key:
                 continue
             value = d.get(key)
-            if value:
+            if value is not None:
                 for f in filters:
                     if f(key, value):
                         return None
diff --git i/plover/translation.py w/plover/translation.py
index 493d63a5..d387dc4c 100644
--- i/plover/translation.py
+++ w/plover/translation.py
@@ -333,7 +333,7 @@ class Translator(object):
                 t.is_retrospective_command = True
                 return t
 
-        if mapping is not None:  # Could be the empty string.
+        if mapping:
             return Translation([stroke], mapping)
         t = self._find_translation_helper(stroke, system.SUFFIX_KEYS)
         if t:
@@ -360,7 +360,7 @@ class Translator(object):
             strokes = list(itertools.chain(*[t.strokes for t in replaced]))
             strokes.append(stroke)
             mapping = self._lookup(strokes, suffixes)
-            if mapping != None:
+            if mapping:
                 t = Translation(strokes, mapping)
                 t.replaced = replaced
                 return t
@@ -368,14 +368,14 @@ class Translator(object):
     def _lookup(self, strokes, suffixes=()):
         dict_key = tuple(s.rtfcre for s in strokes)
         result = self._dictionary.lookup(dict_key)
-        if result != None:
+        if result:
             return result
 
         for key in suffixes:
             if key in strokes[-1].steno_keys:
                 dict_key = (Stroke([key]).rtfcre,)
                 suffix_mapping = self._dictionary.lookup(dict_key)
-                if suffix_mapping is None:
+                if not suffix_mapping:
                     continue
                 keys = strokes[-1].steno_keys[:]
                 keys.remove(key)
@@ -383,7 +383,7 @@ class Translator(object):
                 copy[-1] = Stroke(keys)
                 dict_key = tuple(s.rtfcre for s in copy)
                 main_mapping = self._dictionary.lookup(dict_key)
-                if main_mapping is None:
+                if not main_mapping:
                     continue
                 return main_mapping + ' ' + suffix_mapping