use unix line ending \n as default if empty

src/monty/io.py

@@ -13,6 +13,7 @@
 import os
 import subprocess
 import time
+import warnings
 from pathlib import Path
 from typing import TYPE_CHECKING
 
@@ -80,7 +81,8 @@ def _get_line_ending(
         raise TypeError(f"Unknown file type {type(file).__name__}")
 
     if not first_line:
-        raise ValueError("empty file.")
+        warnings.warn("File empty, use default line ending \n.", stacklevel=2)
+        return "\n"
 
     if first_line.endswith(b"\r\n"):
         return "\r\n"

tests/test_io.py

@@ -65,8 +65,8 @@ def test_empty_file(self):
             test_file = "empty_file.txt"
             open(test_file, "w").close()
 
-            with pytest.raises(ValueError, match="empty file"):
-                _get_line_ending(test_file)
+            with pytest.warns(match="File empty, use default line ending \n"):
+                assert _get_line_ending(test_file) == "\n"
 
     def test_unknown_line_ending(self):
         with ScratchDir("."):
@@ -119,9 +119,10 @@ def test_empty_file(self):
         Make sure an empty file does not throw an error when reverse_readline
         is called, which was a problem with an earlier implementation.
         """
-        with open(os.path.join(TEST_DIR, "empty_file.txt")) as f:
-            for _line in reverse_readline(f):
-                raise ValueError("an empty file is being read!")
+        with pytest.warns(match="File empty, use default line ending \n."):
+            with open(os.path.join(TEST_DIR, "empty_file.txt")) as f:
+                for _line in reverse_readline(f):
+                    raise ValueError("an empty file is being read!")
 
     @pytest.fixture()
     def test_line_ending(self):
@@ -189,8 +190,9 @@ def test_empty_file(self):
         Make sure an empty file does not throw an error when reverse_readline
         is called, which was a problem with an earlier implementation.
         """
-        for _line in reverse_readfile(os.path.join(TEST_DIR, "empty_file.txt")):
-            raise ValueError("an empty file is being read!")
+        with pytest.warns(match="File empty, use default line ending \n."):
+            for _line in reverse_readfile(os.path.join(TEST_DIR, "empty_file.txt")):
+                raise ValueError("an empty file is being read!")
 
     @pytest.fixture
     def test_line_ending(self):