Undocument _InvalidOutput exception

docs/topics/exceptions.rst

@@ -62,17 +62,6 @@ remain disabled. Those components include:
 
 The exception must be raised in the component's ``__init__`` method.
 
-InvalidOutput
--------------
-
-.. exception:: InvalidOutput
-
-This exception can be raised by a downloader or spider middleware to
-indicate that some method returned a value not suported by the processing
-chain.
-See :ref:`topics-spider-middleware` and :ref:`topics-downloader-middleware`
-for a list of supported output values.
-
 NotSupported
 ------------
 

scrapy/core/spidermw.py

@@ -5,7 +5,7 @@ See documentation in docs/topics/spider-middleware.rst
 """
 import six
 from twisted.python.failure import Failure
-from scrapy.exceptions import InvalidOutput
+from scrapy.exceptions import _InvalidOutput
 from scrapy.middleware import MiddlewareManager
 from scrapy.utils.defer import mustbe_deferred
 from scrapy.utils.conf import build_component_list
@@ -42,7 +42,7 @@ class SpiderMiddlewareManager(MiddlewareManager):
                 try:
                     result = method(response=response, spider=spider)
                     if result is not None:
-                        raise InvalidOutput('Middleware {} must return None or raise ' \
+                        raise _InvalidOutput('Middleware {} must return None or raise ' \
                             'an exception, got {}'.format(fname(method), type(result)))
                 except:
                     return scrape_func(Failure(), request, spider)
@@ -50,13 +50,13 @@ class SpiderMiddlewareManager(MiddlewareManager):
 
         def process_spider_exception(_failure):
             exception = _failure.value
-            # don't handle InvalidOutput exception
-            if isinstance(exception, InvalidOutput):
+            # don't handle _InvalidOutput exception
+            if isinstance(exception, _InvalidOutput):
                 return _failure
             for method in self.methods['process_spider_exception']:
                 result = method(response=response, exception=exception, spider=spider)
                 if result is not None and not _isiterable(result):
-                    raise InvalidOutput('Middleware {} must return None or an iterable ' \
+                    raise _InvalidOutput('Middleware {} must return None or an iterable ' \
                         'object, got {}'.format(fname(method), type(result)))
                 # stop exception handling by handing control over to the
                 # process_spider_output chain if an iterable has been returned
@@ -80,7 +80,7 @@ class SpiderMiddlewareManager(MiddlewareManager):
                 if _isiterable(result):
                     result = wrapper(result)
                 else:
-                    raise InvalidOutput('Middleware {} must return an iterable object, ' \
+                    raise _InvalidOutput('Middleware {} must return an iterable object, ' \
                         'got {}'.format(fname(method), type(result)))
             return result
 

scrapy/exceptions.py

@@ -11,9 +11,11 @@ class NotConfigured(Exception):
     """Indicates a missing configuration situation"""
     pass
 
-class InvalidOutput(TypeError):
-    """Indicates an invalid value has been returned
-    by a middleware's processing method"""
+class _InvalidOutput(TypeError):
+    """
+    Indicates an invalid value has been returned by a middleware's processing method.
+    Internal and undocumented, it should not be raised or caught by user code.
+    """
     pass
 
 # HTTP and crawling

tests/test_spidermiddleware.py

@@ -159,7 +159,7 @@ class DoSomethingMiddleware(object):
 
 
 # ================================================================================
-# don't catch InvalidOutput from scrapy's spider middleware manager
+# don't catch _InvalidOutput from scrapy's spider middleware manager
 class InvalidReturnValueFromPreviousMiddlewareInputSpider(LocalhostSpider):
     name = 'invalid_return_value_from_previous_middleware_input'
     custom_settings = {
@@ -318,19 +318,19 @@ class TestSpiderMiddleware(TestCase):
 
     @defer.inlineCallbacks
     def test_process_spider_exception_invalid_return_value_previous_middleware(self):
-        """ don't catch InvalidOutput from middleware """
+        """ don't catch _InvalidOutput from middleware """
         # on middleware's input
         crawler1 = get_crawler(InvalidReturnValueFromPreviousMiddlewareInputSpider)
         with LogCapture() as log1:
             yield crawler1.crawl()
-        self.assertNotIn("InvalidOutput exception caught", str(log1))
-        self.assertIn("'spider_exceptions/InvalidOutput'", str(log1))
+        self.assertNotIn("_InvalidOutput exception caught", str(log1))
+        self.assertIn("'spider_exceptions/_InvalidOutput'", str(log1))
         # on middleware's output
         crawler2 = get_crawler(InvalidReturnValueFromPreviousMiddlewareOutputSpider)
         with LogCapture() as log2:
             yield crawler2.crawl()
-        self.assertNotIn("InvalidOutput exception caught", str(log2))
-        self.assertIn("'spider_exceptions/InvalidOutput'", str(log2))
+        self.assertNotIn("_InvalidOutput exception caught", str(log2))
+        self.assertIn("'spider_exceptions/_InvalidOutput'", str(log2))
 
     @defer.inlineCallbacks
     def test_process_spider_exception_execution_chain(self):