Optimized is_valid_hostname

webssh/utils.py

 import ipaddress
 import re
 
-
 try:
     from types import UnicodeType
 except ImportError:
     UnicodeType = str
 
 
+numeric = re.compile(r'[0-9]+$')
+allowed = re.compile(r'(?!-)[a-z0-9-]{1,63}(?<!-)$', re.IGNORECASE)
+
+
 def to_str(bstr, encoding='utf-8'):
     if isinstance(bstr, bytes):
         return bstr.decode(encoding)
@@ -43,17 +46,16 @@ def is_valid_port(port):
 
 
 def is_valid_hostname(hostname):
-    if hostname[-1] == ".":
+    if hostname[-1] == '.':
         # strip exactly one dot from the right, if present
         hostname = hostname[:-1]
     if len(hostname) > 253:
         return False
 
-    labels = hostname.split(".")
+    labels = hostname.split('.')
 
     # the TLD must be not all-numeric
-    if re.match(r"[0-9]+$", labels[-1]):
+    if numeric.match(labels[-1]):
         return False
 
-    allowed = re.compile(r"(?!-)[a-z0-9-]{1,63}(?<!-)$", re.IGNORECASE)
     return all(allowed.match(label) for label in labels)