From 93482a1f885d8e2e152ea98c671de036bd4e8235 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mike=20F=C3=A4hrmann?= <mike_faehrmann@web.de>
Date: Sun, 3 Dec 2017 01:38:24 +0100
Subject: [PATCH] implement 'util.advance()'

---
 gallery_dl/extractor/seiga.py | 21 ++++++++-------------
 gallery_dl/util.py            |  8 ++++++++
 test/test_util.py             | 12 ++++++++++++
 3 files changed, 28 insertions(+), 13 deletions(-)

diff --git a/gallery_dl/extractor/seiga.py b/gallery_dl/extractor/seiga.py
index f85751d8..210ea303 100644
--- a/gallery_dl/extractor/seiga.py
+++ b/gallery_dl/extractor/seiga.py
@@ -11,7 +11,6 @@
 from .common import Extractor, Message
 from .. import text, util, exception
 from ..cache import cache
-import itertools
 
 
 class SeigaExtractor(Extractor):
@@ -21,20 +20,16 @@ class SeigaExtractor(Extractor):
 
     def __init__(self):
         Extractor.__init__(self)
-        self.startimg = 0
+        self.start_image = 0
 
     def items(self):
         self.login()
         images = iter(self.get_images())
         data = next(images)
 
-        if self.startimg:
-            # consume elements up to 'startimg'
-            next(itertools.islice(images, self.startimg, self.startimg), None)
-
         yield Message.Version, 1
         yield Message.Directory, data
-        for image in images:
+        for image in util.advance(images, self.start_image):
             data.update(image)
             data["extension"] = None
             yield Message.Url, self.get_image_url(data["image_id"]), data
@@ -91,12 +86,12 @@ class SeigaUserExtractor(SeigaExtractor):
     def __init__(self, match):
         SeigaExtractor.__init__(self)
         self.user_id, self.order = match.groups()
-        self.startpage = 1
+        self.start_page = 1
 
     def skip(self, num):
         pages, images = divmod(num, 40)
-        self.startpage += pages
-        self.startimg += images
+        self.start_page += pages
+        self.start_image += images
         return num
 
     def get_metadata(self, page):
@@ -122,14 +117,14 @@ class SeigaUserExtractor(SeigaExtractor):
 
     def get_images(self):
         url = "http://seiga.nicovideo.jp/user/illust/" + self.user_id
-        params = {"sort": self.order, "page": self.startpage,
+        params = {"sort": self.order, "page": self.start_page,
                   "target": "illust_all"}
 
         while True:
             cnt = 0
             page = self.request(url, params=params).text
 
-            if params["page"] == self.startpage:
+            if params["page"] == self.start_page:
                 yield self.get_metadata(page)
 
             for info in text.extract_iter(
@@ -174,7 +169,7 @@ class SeigaImageExtractor(SeigaExtractor):
         self.image_id = match.group(1)
 
     def skip(self, num):
-        self.startimg += num
+        self.start_image += num
         return num
 
     def get_images(self):
diff --git a/gallery_dl/util.py b/gallery_dl/util.py
index 3cf3000c..6834916d 100644
--- a/gallery_dl/util.py
+++ b/gallery_dl/util.py
@@ -20,6 +20,7 @@ import string
 import _string
 import hashlib
 import datetime
+import itertools
 import urllib.parse
 from . import text, exception
 
@@ -100,6 +101,13 @@ def parse_bytes(value, suffixes="bkmgtp"):
         return 0
 
 
+def advance(iterable, num):
+    """"Advance the iterable by 'num' steps"""
+    iterator = iter(iterable)
+    next(itertools.islice(iterator, num, num), None)
+    return iterator
+
+
 def combine_dict(a, b):
     """Recursively combine the contents of b into a"""
     for key, value in b.items():
diff --git a/test/test_util.py b/test/test_util.py
index 137a0f8d..cf972e36 100644
--- a/test/test_util.py
+++ b/test/test_util.py
@@ -205,6 +205,18 @@ class TestOther(unittest.TestCase):
         self.assertEqual(util.parse_bytes("invalid"), 0)
         self.assertEqual(util.parse_bytes(" 123 kb "), 0)
 
+    def test_advance(self):
+        items = range(5)
+
+        self.assertCountEqual(
+            util.advance(items, 0), items)
+        self.assertCountEqual(
+            util.advance(items, 3), range(3, 5))
+        self.assertCountEqual(
+            util.advance(items, 9), [])
+        self.assertCountEqual(
+            util.advance(util.advance(items, 1), 2), range(3, 5))
+
     def test_combine_dict(self):
         self.assertEqual(
             util.combine_dict({}, {}),