[deviantart] use proper exponential backoff on API errors

... and use separate API credentials for unit tests.

gallery_dl/extractor/deviantart.py

@@ -464,29 +464,32 @@ class DeviantartAPI():
     def _call(self, endpoint, params=None, expect_error=False):
         """Call an API endpoint"""
         url = "https://www.deviantart.com/api/v1/oauth2/" + endpoint
-        tries = 1
         while True:
-            if self.delay:
-                time.sleep(self.delay)
+            if self.delay > 0:
+                time.sleep(2 ** (self.delay-1))
 
             self.authenticate()
             response = self.session.get(
                 url, headers=self.headers, params=params)
 
             if response.status_code == 200:
+                if self.delay > 2:
+                    self.delay -= 1
                 break
-            elif response.status_code == 429:
-                self.delay += 1
-                self.log.debug("rate limit (delay: %d)", self.delay)
+
             else:
-                if expect_error:
-                    return None
-                self.delay = 1
-                self.log.debug("http status code %d (%d/3)",
-                               response.status_code, tries)
-            tries += 1
-            if tries > 3:
-                raise Exception(response.text)
+                self.delay += 1
+
+                if response.status_code == 429:
+                    msg = "Rate limit reached"
+                else:
+                    if expect_error:
+                        return None
+                    msg = "API responded with {} {}".format(
+                        response.status_code, response.reason)
+                self.log.warning(
+                    "%s. Using %ds delay.", msg, 2 ** (self.delay-1))
+                self.log.debug(response.text)
         try:
             return response.json()
         except ValueError:

gallery_dl/extractor/luscious.py

@@ -25,7 +25,7 @@ class LusciousAlbumExtractor(AsynchronousExtractor):
         (("https://luscious.net/c/hentai_manga/albums/"
           "okinami-no-koigokoro_277031/view/"), {
             "url": "7e4984a271a1072ac6483e4228a045895aff86f3",
-            "keyword": "76e099479b180420fd5cf820f00c52fe07fda884",
+            "keyword": "e746a3771f4e14bfff81215232a12417d6351ce6",
             "content": "b3a747a6464509440bd0ff6d1267e6959f8d6ff3",
         }),
         ("https://luscious.net/albums/virgin-killer-sweater_282582/", {

test/test_extractors.py

@@ -36,6 +36,9 @@ class TestExtractors(unittest.TestCase):
         config.set(("extractor", "password"), name)
         config.set(("extractor", "nijie", "username"), email)
         config.set(("extractor", "seiga", "username"), email)
+        config.set(("extractor", "deviantart", "client-id"), "7777")
+        config.set(("extractor", "deviantart", "client-secret"),
+                   "ff14994c744d9208e5caeec7aab4a026")
         config.set(("extractor", "tumblr", "api-key"),
                    "0cXoHfIqVzMQcc3HESZSNsVlulGxEXGDTTZCDrRrjaa0jmuTc6")