implement 'keywords-eval' option (#5621)

to allow evaluating 'keywords' values as format strings

docs/configuration.rst

@@ -692,6 +692,17 @@ Description
     Additional name-value pairs to be added to each metadata dictionary.
 
 
+extractor.*.keywords-eval
+-------------------------
+Type
+    ``bool``
+Default
+    ``false``
+Description
+    Evaluate each `keywords <extractor.*.keywords_>`__ ``string`` value
+    as a `format string`_.
+
+
 extractor.*.keywords-default
 ----------------------------
 Type

gallery_dl/job.py

@@ -42,8 +42,9 @@ class Job():
 
         self.extractor = extr
         self.pathfmt = None
-        self.kwdict = {}
         self.status = 0
+        self.kwdict = {}
+        self.kwdict_eval = False
 
         cfgpath = []
         if parent:
@@ -120,7 +121,16 @@ class Job():
         # user-supplied metadata
         kwdict = extr.config("keywords")
         if kwdict:
-            self.kwdict.update(kwdict)
+            if extr.config("keywords-eval"):
+                self.kwdict_eval = []
+                for key, value in kwdict.items():
+                    if isinstance(value, str):
+                        fmt = formatter.parse(value, None, util.identity)
+                        self.kwdict_eval.append((key, fmt.format_map))
+                    else:
+                        self.kwdict[key] = value
+            else:
+                self.kwdict.update(kwdict)
 
     def run(self):
         """Execute or run the job"""
@@ -215,6 +225,9 @@ class Job():
             kwdict.pop(self.metadata_http, None)
         if self.kwdict:
             kwdict.update(self.kwdict)
+        if self.kwdict_eval:
+            for key, valuegen in self.kwdict_eval:
+                kwdict[key] = valuegen(kwdict)
 
     def _init(self):
         self.extractor.initialize()