[path] implement dynamic length directories (#1350)

append directory segments for each item of a list (or general non-string
iterable), which can be returned with the 'I' specifier

gallery_dl/extractor/aryion.py

@@ -19,7 +19,7 @@ BASE_PATTERN = r"(?:https?://)?(?:www\.)?aryion\.com/g4"
 class AryionExtractor(Extractor):
     """Base class for aryion extractors"""
     category = "aryion"
-    directory_fmt = ("{category}", "{user!l}", "{path:J - }")
+    directory_fmt = ("{category}", "{user!l}", "{path:I}")
     filename_fmt = "{id} {title}.{extension}"
     archive_fmt = "{id}"
     cookies_domain = ".aryion.com"

gallery_dl/extractor/bbc.py

@@ -18,8 +18,7 @@ class BbcGalleryExtractor(GalleryExtractor):
     """Extractor for a programme gallery on bbc.co.uk"""
     category = "bbc"
     root = "https://www.bbc.co.uk"
-    directory_fmt = ("{category}", "{path[0]}", "{path[1]}", "{path[2]}",
-                     "{path[3:]:J - /}")
+    directory_fmt = ("{category}", "{path:I}")
     filename_fmt = "{num:>02}.{extension}"
     archive_fmt = "{programme}_{num}"
     pattern = rf"{BASE_PATTERN}[^/?#]+(?!/galleries)(?:/[^/?#]+)?)$"

gallery_dl/path.py

@@ -282,12 +282,20 @@ class PathFormat():
             segments = []
             strip = self.strip
             for fmt in formatters:
-                segment = fmt(kwdict).strip()
-                if strip and segment not in {".", ".."}:
-                    # remove trailing dots and spaces (#647)
-                    segment = segment.rstrip(strip)
-                if segment:
-                    segments.append(self.clean_segment(segment))
+                segment = fmt(kwdict)
+                if segment.__class__ is str:
+                    segment = segment.strip()
+                    if strip and segment not in {".", ".."}:
+                        segment = segment.rstrip(strip)
+                    if segment:
+                        segments.append(self.clean_segment(segment))
+                else:  # assume list
+                    for segment in segment:
+                        segment = segment.strip()
+                        if strip and segment not in {".", ".."}:
+                            segment = segment.rstrip(strip)
+                        if segment:
+                            segments.append(self.clean_segment(segment))
             return segments
         except Exception as exc:
             raise exception.DirectoryFormatError(exc)