[chores] Fixed minor regex warnings

(cherry picked from commit 5400a27)

Author: nemesifier

openwisp_controller/config/base/config.py

@@ -426,7 +426,7 @@ def _should_use_dsa(self):
 
         # Check if the device is using stock OpenWrt.
         openwrt_match = re.search(
-            '[oO][pP][eE][nN][wW][rR][tT]\s*([\d.]+)', self.device.os
+            r'[oO][pP][eE][nN][wW][rR][tT]\s*([\d.]+)', self.device.os
         )
         if openwrt_match:
             if version.parse(openwrt_match.group(1)) >= version.parse('21'):

openwisp_controller/config/validators.py

@@ -2,7 +2,7 @@
 from django.utils.translation import gettext_lazy as _
 
 key_validator = RegexValidator(
-    _lazy_re_compile('^[^\s/\.]+$'),
+    _lazy_re_compile(r'^[^\s/\.]+$'),
     message=_('Key must not contain spaces, dots or slashes.'),
     code='invalid',
 )
@@ -16,9 +16,9 @@
 
 # device name must either be a hostname or a valid mac address
 hostname_regex = (
-    '^([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]{0,61}'
-    '[a-zA-Z0-9])(\.([a-zA-Z0-9]|[a-zA-Z0-9]'
-    '[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9]))*$'
+    r'^([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]{0,61}'
+    r'[a-zA-Z0-9])(\.([a-zA-Z0-9]|[a-zA-Z0-9]'
+    r'[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9]))*$'
 )
 device_name_validator = RegexValidator(
     _lazy_re_compile('{0}|{1}'.format(hostname_regex, mac_address_regex)),

openwisp_controller/connection/commands.py

@@ -65,7 +65,7 @@
                             'type': 'string',
                             'minLength': 6,
                             'maxLength': 30,
-                            'pattern': '[\S]',
+                            'pattern': r'[\S]',
                         }
                     },
                 },