add structure to compute on the fly, but not impoemented yet

text/processing.py

@@ -318,7 +318,7 @@ def __init__(
         self,
         text_file: tk.Path,
         num_lines_per_split: int,
-        num_text_file_lines: int,
+        num_text_file_lines: Optional[int] = None,
         zip_output: bool = True,
     ):
         """
@@ -336,9 +336,12 @@ def __init__(
         self.num_text_file_lines = num_text_file_lines
         self.zip_output = zip_output
 
-        self.num_output_files = self.num_text_file_lines // self.num_lines_per_split + int(
-            bool(self.num_text_file_lines % self.num_lines_per_split)
-        )
+        if num_text_file_lines is not None:
+            self.num_output_files = self.num_text_file_lines // self.num_lines_per_split + int(
+                bool(self.num_text_file_lines % self.num_lines_per_split)
+            )
+        else:
+            raise NotImplementedError
 
         self.out_split_text_files = {
             k: self.output_path(f'split.{k:04}.{"txt.gz" if zip_output else "txt"}')