[formatter] support filesystem paths for \fM

docs/formatting.md

@@ -272,9 +272,10 @@ Starting a format string with '\f<Type> ' allows to set a different format strin
 </tr>
 <tr>
     <td align="center"><code>M</code></td>
-    <td> Name of a Python module followed by one of its functions.
-     This function gets called with the current metadata dict as
-     argument and should return a string.</td>
+    <td>Path or name of a Python module
+        followed by the name of one of its functions.
+        This function gets called with the current metadata dict as
+        argument and should return a string.</td>
     <td><code>\fM my_module:generate_text</code></td>
 </tr>
 </tbody>

gallery_dl/formatter.py

@@ -218,7 +218,7 @@ class ModuleFormatter():
 
     def __init__(self, function_spec, default=NONE, fmt=None):
         module_name, _, function_name = function_spec.partition(":")
-        module = __import__(module_name)
+        module = util.import_file(module_name)
         self.format_map = getattr(module, function_name)
 
 

test/test_formatter.py

@@ -374,7 +374,7 @@ def noarg():
             try:
                 fmt1 = formatter.parse("\fM testmod:gentext")
                 fmt2 = formatter.parse("\fM testmod:lengths")
-                fmt3 = formatter.parse("\fM testmod:noarg")
+                fmt0 = formatter.parse("\fM testmod:noarg")
 
                 with self.assertRaises(AttributeError):
                     formatter.parse("\fM testmod:missing")
@@ -383,11 +383,17 @@ def noarg():
             finally:
                 sys.path.pop(0)
 
+            fmt3 = formatter.parse("\fM " + path + ":gentext")
+            fmt4 = formatter.parse("\fM " + path + ":lengths")
+
         self.assertEqual(fmt1.format_map(self.kwdict), "'Title' by Name")
         self.assertEqual(fmt2.format_map(self.kwdict), "89")
 
+        self.assertEqual(fmt3.format_map(self.kwdict), "'Title' by Name")
+        self.assertEqual(fmt4.format_map(self.kwdict), "89")
+
         with self.assertRaises(TypeError):
-            self.assertEqual(fmt3.format_map(self.kwdict), "")
+            self.assertEqual(fmt0.format_map(self.kwdict), "")
 
     def _run_test(self, format_string, result, default=None, fmt=format):
         fmt = formatter.parse(format_string, default, fmt)