Add a fast path for URL construction when the netloc is the host (#1271)

CHANGES/1271.misc.rst

@@ -0,0 +1 @@
+Improved performance of constructing :class:`~yarl.URL` when the net location is only the host -- by :user:`bdraco`.

yarl/_url.py

@@ -284,14 +284,20 @@ def __new__(
                     else:
                         host = ""
                 host = cls._encode_host(host, validate_host=False)
-                raw_user = cls._REQUOTER(username) if username else username
-                raw_password = cls._REQUOTER(password) if password else password
-                netloc = cls._make_netloc(raw_user, raw_password, host, port)
                 # Remove brackets as host encoder adds back brackets for IPv6 addresses
                 cache["raw_host"] = host[1:-1] if "[" in host else host
-                cache["raw_user"] = raw_user
-                cache["raw_password"] = raw_password
                 cache["explicit_port"] = port
+                if port is None and password is None and username is None:
+                    # Fast path for URLs without user, password and port
+                    netloc = host
+                    cache["raw_user"] = None
+                    cache["raw_password"] = None
+                else:
+                    raw_user = cls._REQUOTER(username) if username else username
+                    raw_password = cls._REQUOTER(password) if password else password
+                    netloc = cls._make_netloc(raw_user, raw_password, host, port)
+                    cache["raw_user"] = raw_user
+                    cache["raw_password"] = raw_password
 
             if path:
                 path = cls._PATH_REQUOTER(path)
@@ -368,7 +374,10 @@ def build(
             elif host:
                 if port is not None:
                     port = None if port == DEFAULT_PORTS.get(scheme) else port
-                netloc = cls._make_netloc(user, password, host, port)
+                if port is None and user is None and password is None:
+                    netloc = host
+                else:
+                    netloc = cls._make_netloc(user, password, host, port)
             else:
                 netloc = ""
         else:  # not encoded
@@ -384,7 +393,10 @@ def build(
             if _host is not None:
                 if port is not None:
                     port = None if port == DEFAULT_PORTS.get(scheme) else port
-                netloc = cls._make_netloc(user, password, _host, port, True)
+                if port is None and user is None and password is None:
+                    netloc = _host
+                else:
+                    netloc = cls._make_netloc(user, password, _host, port, True)
 
             path = cls._PATH_QUOTER(path) if path else path
             if path and netloc: