[image-pipeline] image settings with class name

allow to have image settings with class name, so that settings for user defined ImagePipeline
subclasses can be defined easily.

docs/topics/media-pipeline.rst

@@ -191,9 +191,9 @@ For the Images Pipeline, set :setting:`IMAGES_URLS_FIELD` and/or
 If you need something more complex and want to override the custom pipeline
 behaviour, see :ref:`topics-media-pipeline-override`.
 
-.. note:: If you have multiple image pipelines and you want to have different settings in different pipelines
-   you can either set class attributes in pipeline object or add custom settings keys and load them at pipeline
-   initialization.
+.. note:: If you have multiple image pipelines inheriting from ImagePipeline and you want to have different settings in different pipelines
+   you can set setting keys preceded with uppercase name of your pipeline class. E.g. if your pipeline is called
+   MyPipeline and you want to have custom IMAGES_URLS_FIELD you define setting MYPIPELINE_IMAGES_URLS_FIELD.
 
 
 Additional features

scrapy/pipelines/images.py

@@ -50,12 +50,27 @@ class ImagesPipeline(FilesPipeline):
         if isinstance(settings, dict) or settings is None:
             settings = Settings(settings)
 
-        self.expires = settings.getint('IMAGES_EXPIRES', self.EXPIRES)
-        self.images_urls_field = settings.get('IMAGES_URLS_FIELD', self.IMAGES_URLS_FIELD)
-        self.images_result_field = settings.get('IMAGES_RESULT_FIELD', self.IMAGES_RESULT_FIELD)
-        self.min_width = settings.getint('IMAGES_MIN_WIDTH', self.MIN_WIDTH)
-        self.min_height = settings.getint('IMAGES_MIN_HEIGHT', self.MIN_HEIGHT)
-        self.thumbs = settings.get('IMAGES_THUMBS', self.THUMBS)
+        def key_for_pipe(key):
+            """
+            Allow setting settings for user defined ImagePipelines that inherit from base.
+
+            User can define setting key:
+
+            MYPIPELINENAME_IMAGE_SETTING_NAME = <some value>
+
+            and it will override default settings and class attributes.
+            """
+            class_name = self.__class__.__name__
+            if class_name == "ImagesPipeline":
+                return key
+            return "{}_{}".format(class_name.upper(), key)
+
+        self.expires = settings.getint(key_for_pipe('IMAGES_EXPIRES'), self.EXPIRES)
+        self.images_urls_field = settings.get(key_for_pipe('IMAGES_URLS_FIELD'), self.IMAGES_URLS_FIELD)
+        self.images_result_field = settings.get(key_for_pipe('IMAGES_RESULT_FIELD'), self.IMAGES_RESULT_FIELD)
+        self.min_width = settings.getint(key_for_pipe('IMAGES_MIN_WIDTH'), self.MIN_WIDTH)
+        self.min_height = settings.getint(key_for_pipe('IMAGES_MIN_HEIGHT'), self.MIN_HEIGHT)
+        self.thumbs = settings.get(key_for_pipe('IMAGES_THUMBS'), self.THUMBS)
 
     @classmethod
     def from_settings(cls, settings):

tests/test_pipeline_images.py

@@ -265,7 +265,7 @@ class ImagesPipelineTestCaseCustomSettings(unittest.TestCase):
         pipeline = UserDefinedImagePipeline.from_settings(Settings({"IMAGES_STORE": self.tempdir}))
         self.assertEqual(pipeline.min_width, 1000)
 
-    def test_class_attrs_not_preserved_if_settings_defined(self):
+    def test_class_attrs_preserved_if_only_global_settings_defined(self):
 
         class UserDefinedImagePipeline(ImagesPipeline):
             MIN_WIDTH = 1000
@@ -277,7 +277,21 @@ class ImagesPipelineTestCaseCustomSettings(unittest.TestCase):
 
         # If image settings are defined they override class attributes.
         pipeline = UserDefinedImagePipeline.from_settings(Settings(settings))
-        self.assertEqual(pipeline.min_width, 90)
+        self.assertEqual(pipeline.min_width, 1000)
+
+    def test_settings_multiple_pipelilines(self):
+        # If user has multiple pipelines he can define setting keys preceded with
+        # pipeline class name.
+        class UserDefinedPipeline(ImagesPipeline):
+            pass
+
+        settings = {
+            "IMAGES_MIN_WIDTH": 10,
+            "USERDEFINEDPIPELINE_IMAGES_MIN_WIDTH": 1999,
+            "IMAGES_STORE": self.tempdir
+        }
+        user_pipeline = UserDefinedPipeline.from_settings(Settings(settings))
+        self.assertEqual(user_pipeline.min_width, 1999)
 
 
 def _create_image(format, *a, **kw):