[postprocessor:metadata] accept a string-list for 'content-format'

(closes #1080)

docs/configuration.rst

@@ -2053,9 +2053,10 @@ Description
 metadata.content-format
 -----------------------
 Type
-    ``string``
+    ``string`` or ``list`` of ``strings``
 Example
-    ``"tags:\n\n{tags:J\n}\n"``
+    * ``"tags:\n\n{tags:J\n}\n"``
+    * ``["tags:", "", "{tags:J\n}"]``
 Description
     Custom format string to build the content of metadata files with.
 

gallery_dl/postprocessor/metadata.py

@@ -22,6 +22,8 @@ class MetadataPP(PostProcessor):
         if mode == "custom":
             self.write = self._write_custom
             cfmt = options.get("content-format") or options.get("format")
+            if isinstance(cfmt, list):
+                cfmt = "\n".join(cfmt) + "\n"
             self.contentfmt = util.Formatter(cfmt).format_map
             ext = "txt"
         elif mode == "tags":

test/test_postprocessor.py

@@ -235,10 +235,8 @@ class MetadataTest(BasePostprocessorTest):
         self.assertEqual(self._output(m), "foo\nbar\nbaz\n")
 
     def test_metadata_custom(self):
-        pp = self._create(
-            {"mode": "custom", "format": "{foo}\n{missing}\n"},
-            {"foo": "bar"},
-        )
+        def test(pp_info):
+            pp = self._create(pp_info, {"foo": "bar"})
             self.assertEqual(pp.write, pp._write_custom)
             self.assertEqual(pp.extension, "txt")
             self.assertTrue(pp.contentfmt)
@@ -248,6 +246,10 @@ class MetadataTest(BasePostprocessorTest):
                 pp.run(self.pathfmt)
             self.assertEqual(self._output(m), "bar\nNone\n")
 
+        test({"mode": "custom", "content-format": "{foo}\n{missing}\n"})
+        test({"mode": "custom", "content-format": ["{foo}", "{missing}"]})
+        test({"mode": "custom", "format": "{foo}\n{missing}\n"})
+
     def test_metadata_extfmt(self):
         pp = self._create({
             "extension"       : "ignored",