PI-3677: Remove regex from standard names check (#3679)

* Remove regex from standard names check

* remove duplicated test

* Added test cases for none, empty and only spaces

* Remove duplicated test

* Address comments

* Blackify code

lib/iris/_cube_coord_common.py

@@ -46,7 +46,6 @@ def get_valid_standard_name(name):
     # modifier, separated by one or more blank spaces
 
     if name is not None:
-        name_is_valid = False
         # Supported standard name modifiers. Ref: [CF] Appendix C.
         valid_std_name_modifiers = [
             "detection_minimum",
@@ -55,19 +54,21 @@ def get_valid_standard_name(name):
             "status_flag",
         ]
 
-        valid_name_pattern = re.compile(r"""^([a-zA-Z_]+)( *)([a-zA-Z_]*)$""")
-        name_groups = valid_name_pattern.match(name)
-
+        name_groups = name.split(maxsplit=1)
         if name_groups:
-            std_name, whitespace, std_name_modifier = name_groups.groups()
-            if (std_name in iris.std_names.STD_NAMES) and (
-                bool(whitespace)
-                == (std_name_modifier in valid_std_name_modifiers)
-            ):
-                name_is_valid = True
-
-        if name_is_valid is False:
-            raise ValueError("{!r} is not a valid standard_name".format(name))
+            std_name = name_groups[0]
+            name_is_valid = std_name in iris.std_names.STD_NAMES
+            try:
+                std_name_modifier = name_groups[1]
+            except IndexError:
+                pass  # No modifier
+            else:
+                name_is_valid &= std_name_modifier in valid_std_name_modifiers
+
+            if not name_is_valid:
+                raise ValueError(
+                    "{!r} is not a valid standard_name".format(name)
+                )
 
     return name
 

lib/iris/tests/unit/cube_coord_common/test_get_valid_standard_name.py

@@ -19,10 +19,26 @@ class Test(tests.IrisTest):
     def setUp(self):
         self.emsg = "'{}' is not a valid standard_name"
 
+    def test_pass_thru_none(self):
+        name = None
+        self.assertEqual(get_valid_standard_name(name), name)
+
+    def test_pass_thru_empty(self):
+        name = ""
+        self.assertEqual(get_valid_standard_name(name), name)
+
+    def test_pass_thru_whitespace(self):
+        name = "       "
+        self.assertEqual(get_valid_standard_name(name), name)
+
     def test_valid_standard_name(self):
         name = "air_temperature"
         self.assertEqual(get_valid_standard_name(name), name)
 
+    def test_standard_name_alias(self):
+        name = "atmosphere_optical_thickness_due_to_pm1_ambient_aerosol"
+        self.assertEqual(get_valid_standard_name(name), name)
+
     def test_invalid_standard_name(self):
         name = "not_a_standard_name"
         with self.assertRaisesRegex(ValueError, self.emsg.format(name)):