Repository: ytdl-org/youtube-dl

Issue:
Downloads all pages of the playlist even though only the first is needed
I was wondering whether youtube-dl can't be more smart when using playlist-start and playlist-end. When using with playlists like http://www.youtube.com/user/ANNnewsCH/videos it first downloads all ids, even though there are thousands, before it finally decides on using only the first 10. Is it not possible to only download the ids needed? The same thing happens with long playlists.



Discussion:

Resolving patch:
diff --git a/youtube_dl/YoutubeDL.py b/youtube_dl/YoutubeDL.py
--- a/youtube_dl/YoutubeDL.py
+++ b/youtube_dl/YoutubeDL.py
@@ -39,6 +39,7 @@
     locked_file,
     make_HTTPS_handler,
     MaxDownloadsReached,
+    PagedList,
     PostProcessingError,
     platform_name,
     preferredencoding,
@@ -575,19 +576,27 @@ def make_result(embedded_info):
 
             playlist_results = []
 
-            n_all_entries = len(ie_result['entries'])
             playliststart = self.params.get('playliststart', 1) - 1
             playlistend = self.params.get('playlistend', None)
             # For backwards compatibility, interpret -1 as whole list
             if playlistend == -1:
                 playlistend = None
 
-            entries = ie_result['entries'][playliststart:playlistend]
-            n_entries = len(entries)
-
-            self.to_screen(
-                "[%s] playlist '%s': Collected %d video ids (downloading %d of them)" %
-                (ie_result['extractor'], playlist, n_all_entries, n_entries))
+            if isinstance(ie_result['entries'], list):
+                n_all_entries = len(ie_result['entries'])
+                entries = ie_result['entries'][playliststart:playlistend]
+                n_entries = len(entries)
+                self.to_screen(
+                    "[%s] playlist %s: Collected %d video ids (downloading %d of them)" %
+                    (ie_result['extractor'], playlist, n_all_entries, n_entries))
+            else:
+                assert isinstance(ie_result['entries'], PagedList)
+                entries = ie_result['entries'].getslice(
+                    playliststart, playlistend)
+                n_entries = len(entries)
+                self.to_screen(
+                    "[%s] playlist %s: Downloading %d videos" %
+                    (ie_result['extractor'], playlist, n_entries))
 
             for i, entry in enumerate(entries, 1):
                 self.to_screen('[download] Downloading video #%s of %s' % (i, n_entries))
diff --git a/youtube_dl/extractor/youtube.py b/youtube_dl/extractor/youtube.py
--- a/youtube_dl/extractor/youtube.py
+++ b/youtube_dl/extractor/youtube.py
@@ -27,6 +27,7 @@
     get_element_by_id,
     get_element_by_attribute,
     ExtractorError,
+    PagedList,
     RegexNotFoundError,
     unescapeHTML,
     unified_strdate,
@@ -1580,44 +1581,35 @@ def _real_extract(self, url):
         # page by page until there are no video ids - it means we got
         # all of them.
 
-        url_results = []
-
-        for pagenum in itertools.count(0):
+        def download_page(pagenum):
             start_index = pagenum * self._GDATA_PAGE_SIZE + 1
 
             gdata_url = self._GDATA_URL % (username, self._GDATA_PAGE_SIZE, start_index)
-            page = self._download_webpage(gdata_url, username,
-                                          u'Downloading video ids from %d to %d' % (start_index, start_index + self._GDATA_PAGE_SIZE))
+            page = self._download_webpage(
+                gdata_url, username,
+                u'Downloading video ids from %d to %d' % (
+                    start_index, start_index + self._GDATA_PAGE_SIZE))
 
             try:
                 response = json.loads(page)
             except ValueError as err:
                 raise ExtractorError(u'Invalid JSON in API response: ' + compat_str(err))
             if 'entry' not in response['feed']:
-                # Number of videos is a multiple of self._MAX_RESULTS
-                break
+                return
 
             # Extract video identifiers
             entries = response['feed']['entry']
             for entry in entries:
                 title = entry['title']['$t']
                 video_id = entry['id']['$t'].split('/')[-1]
-                url_results.append({
+                yield {
                     '_type': 'url',
                     'url': video_id,
                     'ie_key': 'Youtube',
                     'id': 'video_id',
                     'title': title,
-                })
-
-            # A little optimization - if current page is not
-            # "full", ie. does not contain PAGE_SIZE video ids then
-            # we can assume that this page is the last one - there
-            # are no more ids on further pages - no need to query
-            # again.
-
-            if len(entries) < self._GDATA_PAGE_SIZE:
-                break
+                }
+        url_results = PagedList(download_page, self._GDATA_PAGE_SIZE)
 
         return self.playlist_result(url_results, playlist_title=username)
 
diff --git a/youtube_dl/utils.py b/youtube_dl/utils.py
--- a/youtube_dl/utils.py
+++ b/youtube_dl/utils.py
@@ -6,6 +6,7 @@
 import email.utils
 import errno
 import gzip
+import itertools
 import io
 import json
 import locale
@@ -1161,3 +1162,46 @@ def check_executable(exe, args=[]):
     except OSError:
         return False
     return exe
+
+
+class PagedList(object):
+    def __init__(self, pagefunc, pagesize):
+        self._pagefunc = pagefunc
+        self._pagesize = pagesize
+
+    def getslice(self, start=0, end=None):
+        res = []
+        for pagenum in itertools.count(start // self._pagesize):
+            firstid = pagenum * self._pagesize
+            nextfirstid = pagenum * self._pagesize + self._pagesize
+            if start >= nextfirstid:
+                continue
+
+            page_results = list(self._pagefunc(pagenum))
+
+            startv = (
+                start % self._pagesize
+                if firstid <= start < nextfirstid
+                else 0)
+
+            endv = (
+                ((end - 1) % self._pagesize) + 1
+                if (end is not None and firstid <= end <= nextfirstid)
+                else None)
+
+            if startv != 0 or endv is not None:
+                page_results = page_results[startv:endv]
+            res.extend(page_results)
+
+            # A little optimization - if current page is not "full", ie. does
+            # not contain page_size videos then we can assume that this page
+            # is the last one - there are no more ids on further pages -
+            # i.e. no need to query again.
+            if len(page_results) + startv < self._pagesize:
+                break
+
+            # If we got the whole page, but the next page is not interesting,
+            # break out early as well
+            if end == nextfirstid:
+                break
+        return res


Test patch:
diff --git a/test/test_utils.py b/test/test_utils.py
--- a/test/test_utils.py
+++ b/test/test_utils.py
@@ -18,6 +18,7 @@
     find_xpath_attr,
     get_meta_content,
     orderedSet,
+    PagedList,
     parse_duration,
     sanitize_filename,
     shell_quote,
@@ -200,5 +201,26 @@ def test_parse_duration(self):
         self.assertEqual(parse_duration('9:12:43'), 33163)
         self.assertEqual(parse_duration('x:y'), None)
 
+    def test_paged_list(self):
+        def testPL(size, pagesize, sliceargs, expected):
+            def get_page(pagenum):
+                firstid = pagenum * pagesize
+                upto = min(size, pagenum * pagesize + pagesize)
+                for i in range(firstid, upto):
+                    yield i
+
+            pl = PagedList(get_page, pagesize)
+            got = pl.getslice(*sliceargs)
+            self.assertEqual(got, expected)
+
+        testPL(5, 2, (), [0, 1, 2, 3, 4])
+        testPL(5, 2, (1,), [1, 2, 3, 4])
+        testPL(5, 2, (2,), [2, 3, 4])
+        testPL(5, 2, (4,), [4])
+        testPL(5, 2, (0, 3), [0, 1, 2])
+        testPL(5, 2, (1, 4), [1, 2, 3])
+        testPL(5, 2, (2, 99), [2, 3, 4])
+        testPL(5, 2, (20, 99), [])
+
 if __name__ == '__main__':
     unittest.main()