diff --git a/django/core/mail/message.py b/django/core/mail/message.py
index 20432b05afd..eb10ff1b730 100644
--- a/django/core/mail/message.py
+++ b/django/core/mail/message.py
@@ -256,9 +256,9 @@ class EmailMessage:
         msg['From'] = self.extra_headers.get('From', self.from_email)
         msg['To'] = self.extra_headers.get('To', ', '.join(map(str, self.to)))
         if self.cc:
-            msg['Cc'] = ', '.join(map(str, self.cc))
+            msg['Cc'] = ', '.join(str(cc) for cc in self.cc)
         if self.reply_to:
-            msg['Reply-To'] = self.extra_headers.get('Reply-To', ', '.join(map(str, self.reply_to)))
+            msg['Reply-To'] = self.extra_headers.get('Reply-To', ', '.join(str(r) for r in self.reply_to))
 
         # Email header names are case-insensitive (RFC 2045), so we have to
         # accommodate that when doing comparisons.
diff --git a/django/template/loaders/cached.py b/django/template/loaders/cached.py
index 20abe21b354..b0799a2d0ed 100644
--- a/django/template/loaders/cached.py
+++ b/django/template/loaders/cached.py
@@ -85,7 +85,7 @@ class Loader(BaseLoader):
             if matching:
                 skip_prefix = self.generate_hash(matching)
 
-        return '-'.join(filter(bool, [str(template_name), skip_prefix, dirs_prefix]))
+        return '-'.join(s for s in (str(template_name), skip_prefix, dirs_prefix) if s)
 
     def generate_hash(self, values):
         return hashlib.sha1(force_bytes('|'.join(values))).hexdigest()