[formatter] change 'L'/length conversion to 'n'

docs/formatting.md

@@ -117,9 +117,9 @@ Conversion specifiers allow to *convert* the value to a different form or type.
     <td><code>["sun", "tree", "water"]</code></td>
 </tr>
 <tr>
-    <td align="center"><code>L</code></td>
+    <td align="center"><code>n</code></td>
     <td>Return the <a href="https://docs.python.org/3/library/functions.html#len" rel="nofollow">length</a> of a value</td>
-    <td><code>{foo!L}</code></td>
+    <td><code>{foo!n}</code></td>
     <td><code>7</code></td>
 </tr>
 <tr>

gallery_dl/formatter.py

@@ -484,7 +484,7 @@ _CONVERSIONS = {
     "C": string.capwords,
     "j": util.json_dumps,
     "t": str.strip,
-    "L": len,
+    "n": len,
     "T": util.datetime_to_timestamp_string,
     "d": text.parse_timestamp,
     "D": util.to_datetime,

test/test_formatter.py

@@ -73,9 +73,9 @@ class TestFormatter(unittest.TestCase):
         self._run_test("{l!j}", '["a","b","c"]')
         self._run_test("{dt!j}", '"2010-01-01 00:00:00"')
         self._run_test("{a!g}", "hello-world")
-        self._run_test("{a!L}", 11)
-        self._run_test("{l!L}", 3)
-        self._run_test("{d!L}", 3)
+        self._run_test("{a!n}", 11)
+        self._run_test("{l!n}", 3)
+        self._run_test("{d!n}", 3)
         self._run_test("{i_str!i}", 12345)
         self._run_test("{i_str!f}", 12345.0)
         self._run_test("{f_str!f}", 12.45)