Refactor to only sort once

Rather than doing the sort every time an instance is initiated, we can
speed things up by just doing it the once when the app starts up.

app/utils.py

@@ -445,31 +445,33 @@ class GovernmentDomain:
 
     with open('{}/domains.yml'.format(_dir_path)) as domains:
         domains = yaml.safe_load(domains)
+        domain_names = sorted(domains.keys(), key=len)
 
     def __init__(self, email_address_or_domain):
 
         try:
-            self._match = sorted(
-                (
-                    domain for domain in self.domains.keys()
-                    if self._domain_matches(email_address_or_domain, domain)
-                ),
-                key=len
-            )[0]
-        except IndexError:
+            self._match = next(filter(
+                self.get_matching_function(email_address_or_domain),
+                self.domain_names,
+            ))
+        except StopIteration:
             raise NotGovernmentDomain()
 
         self.owner, self.sector, self.agreement_signed = self._get_details_of_domain()
 
     @staticmethod
-    def _domain_matches(email_address_or_domain, domain):
+    def get_matching_function(email_address_or_domain):
 
         email_address_or_domain = email_address_or_domain.lower()
 
-        return (email_address_or_domain == domain) or re.search(
-            "[\.|@]({})$".format(domain.replace(".", "\.")),
-            email_address_or_domain
-        )
+        def fn(domain):
+
+            return (email_address_or_domain == domain) or re.search(
+                "[\.|@]({})$".format(domain.replace(".", "\.")),
+                email_address_or_domain
+            )
+
+        return fn
 
     def _get_details_of_domain(self):