ShellParser: Prefix output filenames starting with a number

The `format_link_label` now checks whether the filename starts with a
number, in which case the link label is prefixed with `aiida_shell_`
because Python identifiers cannot start with a number.

src/aiida_shell/parsers/shell.py

@@ -57,13 +57,17 @@ def exit_code(self, key: str, **kwargs: t.Any) -> ExitCode:
     def format_link_label(filename: str) -> str:
         """Format the link label from a given filename.
 
-        Valid link labels can only contain alphanumeric characters and underscores, without consecutive underscores. So
-        all characters that are not alphanumeric or an underscore are converted to underscores, where consecutive
-        underscores are merged into one.
+        Valid link labels can only contain alphanumeric characters and underscores, without consecutive underscores.
+        They can also not start with a number. So all characters that are not alphanumeric or an underscore are
+        converted to underscores, where consecutive underscores are merged into one. Filenames that start with a number
+        are prefixed with ``aiida_shell_``.
 
         :param filename: The filename.
         :returns: The link label.
         """
+        if re.match('^[0-9]+.*', filename):
+            filename = f'aiida_shell_{filename}'
+
         alphanumeric = re.sub('[^0-9a-zA-Z_]+', '_', filename)
         link_label = re.sub('_[_]+', '_', alphanumeric)
         return link_label

tests/parsers/test_shell.py

@@ -120,13 +120,14 @@ def test_outputs_missing(parse_calc_job, create_retrieved_temporary):
     (
         ('filename-with-dashes.txt', 'filename_with_dashes_txt'),
         ('file@@name.txt', 'file_name_txt'),
+        ('123startingnumbers', 'aiida_shell_123startingnumbers'),
     ),
 )
 def test_outputs_link_labels(parse_calc_job, create_retrieved_temporary, filename, link_label):
     """Test that filenames are converted into valid link labels.
 
     Any characters that are non-alphanumeric or underscores should be converted to underscores where consecutive
-    underscores are merged into one.
+    underscores are merged into one. Filenames starting with a number are prefixed with ``aiida_shell_``.
     """
     files = {
         filename: 'content_a',
@@ -138,6 +139,7 @@ def test_outputs_link_labels(parse_calc_job, create_retrieved_temporary, filenam
     assert calcfunction.is_finished_ok
 
     for content in files.values():
+        assert link_label in results
         assert isinstance(results[link_label], SinglefileData)
         assert results[link_label].get_content() == content