Address review comments.

src/allmydata/test/test_encodingutil.py

@@ -53,7 +53,9 @@ if __name__ == "__main__":
         for fname in TEST_FILENAMES:
             open(os.path.join(tmpdir, fname), 'w').close()
 
-        # Use Unicode API under Windows or MacOS X
+        # On Python 2, listing directories returns unicode under Windows or
+        # MacOS X if the input is unicode. On Python 3, it always returns
+        # Unicode.
         if PY2 and sys.platform in ('win32', 'darwin'):
             dirlist = os.listdir(unicode(tmpdir))
         else:

src/allmydata/util/encodingutil.py

@@ -214,6 +214,9 @@ def _unicode_escape(m, quote_newlines):
         return u'\\x%02x' % (codepoint,)
 
 def _str_escape(m, quote_newlines):  # TODO rename to _bytes_escape
+    """
+    Takes a re match on bytes, the result is escaped bytes of group(0).
+    """
     c = m.group(0)
     if c == b'"' or c == b'$' or c == b'`' or c == b'\\':
         return b'\\' + c