Fix missing f's.

1 files changed, 1 insertions, 1 deletions

diff --git a/arper.py b/arper.py
index a4e8d3e..696bf97 100644
--- a/arper.py
+++ b/arper.py
@@ -60,7 +60,7 @@ class Arper(persistent.Persistent):
             self.update_from_arp_scan()
             self.update_from_arp()
         if len(self.state) < config.config['arper_min_entries_to_be_valid']:
-            raise Exception('Arper didn\'t find enough entries; only got {len(self.state)}.')
+            raise Exception(f'Arper didn\'t find enough entries; only got {len(self.state)}.')
 
     def update_from_arp_scan(self):
         network_spec = site_config.get_config().network