[job] add 'init' option

docs/configuration.rst

@@ -666,6 +666,28 @@ Note
     is *required*
 
 
+extractor.*.init
+----------------
+Type
+    * ``bool``
+    * ``string``
+Default
+    ``false``
+Description
+    | Controls when to initialize extractor internals.
+    | (
+      `postprocessors <extractor.*.postprocessors_>`_,
+      `archives <extractor.*.archive_>`_,
+      `path-*` options, etc
+      )
+
+    ``true``
+        Initialize everything immediately upon extractor start
+    ``false`` | ``"lazy"``
+        Initialize data structures when processing the first ``post``
+        or not at all when an extractor never yields a ``post``.
+
+
 extractor.*.input
 -----------------
 Type

docs/gallery-dl.conf

@@ -85,6 +85,7 @@
         "sleep-429"      : 60.0,
 
         "actions": [],
+        "init"   : "lazy",
         "input"  : null,
         "netrc"  : false,
         "extension-map": {

gallery_dl/job.py

@@ -274,6 +274,10 @@ class Job():
         self.pred_post = self._prepare_predicates("post", False)
         self.pred_queue = self._prepare_predicates("chapter", False)
 
+        init = self.extractor.config("init", False)
+        if init and init != "lazy":
+            self.initialize()
+
     def _prepare_predicates(self, target, skip):
         predicates = []
         extr = self.extractor