python: use missing

Author: scivision

+stdlib/has_python.m

@@ -32,7 +32,9 @@
   return
 end
 
-y = ~isempty(stdlib.python_version());
+v = stdlib.python_version();
+y = ~ismissing(v) && ~isempty(v);
 
 py_enable = y;
+
 end

+stdlib/private/pvt_python_version.m

@@ -1,6 +1,6 @@
 function v = pvt_python_version()
 
-v = [];
+v = missing;
 
 pe = pyenv();
 % e.g. bad lexical cast: source type value could not be interpreted as target

+stdlib/python_home.m

@@ -6,7 +6,7 @@
   pe = pyenv();
   h = pe.Home;
 catch
-  h = string.empty;
+  h = missing;
 end
 
 end

+stdlib/python_version.m

@@ -18,7 +18,7 @@
 
 persistent stdlib_py_version pyv_cached
 
-msg = '';
+msg = missing;
 
 if isempty(pyv_cached)
   pyv_cached = false;

test/TestLang.m

@@ -14,7 +14,6 @@ function test_python_home(tc)
 tc.assumeTrue(stdlib.has_python(), 'Python not available')
 
 r = stdlib.python_home();
-tc.verifyNotEmpty(r)
 tc.verifyClass(r, 'string')
 end