diff --git a/rest_framework/authentication.py b/rest_framework/authentication.py
index 3f3bd2227c..971d80983f 100644
--- a/rest_framework/authentication.py
+++ b/rest_framework/authentication.py
@@ -150,10 +150,10 @@ def dummy_get_response(request):  # pragma: no cover
 
 class TokenAuthentication(BaseAuthentication):
     """
-    Simple token based authentication.
+    Simple token-based authentication.
 
     Clients should authenticate by passing the token key in the "Authorization"
-    HTTP header, prepended with the string "Token ".  For example:
+    HTTP header, prepended with the string "Token ". For example:
 
         Authorization: Token 401f7ac837da42b97f613d789819ff93537bee6a
     """
@@ -167,31 +167,19 @@ def get_model(self):
         from rest_framework.authtoken.models import Token
         return Token
 
-    """
-    A custom token model may be used, but must have the following properties.
-
-    * key -- The string identifying the token
-    * user -- The user to which the token belongs
-    """
-
     def authenticate(self, request):
         auth = get_authorization_header(request).split()
 
-        if not auth or auth[0].lower() != self.keyword.lower().encode():
+        if len(auth) != 2 or auth[0].lower() != self.keyword.lower().encode():
             return None
-
-        if len(auth) == 1:
-            msg = _('Invalid token header. No credentials provided.')
-            raise exceptions.AuthenticationFailed(msg)
-        elif len(auth) > 2:
-            msg = _('Invalid token header. Token string should not contain spaces.')
-            raise exceptions.AuthenticationFailed(msg)
-
+        
+        token = auth[1]
         try:
-            token = auth[1].decode()
+            token = token.decode()
         except UnicodeError:
-            msg = _('Invalid token header. Token string should not contain invalid characters.')
-            raise exceptions.AuthenticationFailed(msg)
+            raise exceptions.AuthenticationFailed(
+                _('Invalid token header. Token string should not contain invalid characters.')
+            )
 
         return self.authenticate_credentials(token)
 
@@ -205,7 +193,7 @@ def authenticate_credentials(self, key):
         if not token.user.is_active:
             raise exceptions.AuthenticationFailed(_('User inactive or deleted.'))
 
-        return (token.user, token)
+        return token.user, token
 
     def authenticate_header(self, request):
         return self.keyword