improve --clear-cache (#1230)

Allow for an optional argument to only delete cached entries from
a specific module.

delete all cache entries
$ gallery-dl --clear-cache
or
$ gallery-dl --clear-cache all

only delete entries for instagram
$ gallery-dl --clear-cache instagram

gallery_dl/__init__.py

@@ -186,7 +186,7 @@ def main():
         elif args.clear_cache:
             from . import cache
             log = logging.getLogger("cache")
-            cnt = cache.clear()
+            cnt = cache.clear(args.clear_cache)
 
             if cnt is None:
                 log.error("Database file not available")

gallery_dl/cache.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-# Copyright 2016-2020 Mike Fährmann
+# Copyright 2016-2021 Mike Fährmann
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 as
@@ -168,24 +168,33 @@ def wrap(func):
     return wrap
 
 
-def clear():
-    """Delete all database entries"""
+def clear(module="all"):
+    """Delete database entries for 'module'"""
     db = DatabaseCacheDecorator.db
+    if not db:
+        return None
 
-    if db:
-        rowcount = 0
-        cursor = db.cursor()
-        try:
+    rowcount = 0
+    cursor = db.cursor()
+    module = module.lower()
+
+    try:
+        if module == "all":
             cursor.execute("DELETE FROM data")
-        except sqlite3.OperationalError:
-            pass  # database is not initialized,  can't be modified, etc.
         else:
-            rowcount = cursor.rowcount
-            db.commit()
+            cursor.execute(
+                "DELETE FROM data "
+                "WHERE key LIKE 'gallery_dl.extractor.' || ? || '.%'",
+                (module,)
+            )
+    except sqlite3.OperationalError:
+        pass  # database is not initialized,  can't be modified, etc.
+    else:
+        rowcount = cursor.rowcount
+        db.commit()
+        if rowcount:
             cursor.execute("VACUUM")
-        return rowcount
-
-    return None
+    return rowcount
 
 
 def _path():

gallery_dl/option.py

@@ -114,7 +114,7 @@ def build_parser():
     )
     general.add_argument(
         "--clear-cache",
-        dest="clear_cache", action="store_true",
+        dest="clear_cache", metavar="MODULE", nargs="?", const="all",
         help="Delete all cached login sessions, cookies, etc.",
     )