preserve newlines (#681)

* preserve newlines

* fixup test

.pre-commit-config.yaml

@@ -6,6 +6,7 @@ repos:
     rev: v4.0.1
     hooks:
       - id: end-of-file-fixer
+        exclude: ^tests/data/
       - id: requirements-txt-fixer
       - id: trailing-whitespace
       - id: debug-statements
@@ -91,4 +92,4 @@ repos:
     rev: 0.5.0
     hooks:
       - id: nbstripout
-        exclude: ^tests/data/databricks_notebook\.ipynb$
+        exclude: ^tests/data/(databricks_notebook|notebook_for_testing)\.ipynb$

nbqa/replace_source.py

@@ -192,7 +192,8 @@ def mutate(
         Whether mutation actually happened.
     """
     with open(notebook, encoding="utf-8") as handle:
-        notebook_json = json.loads(handle.read())
+        notebook_txt = handle.read()
+    notebook_json = json.loads(notebook_txt)
     original_notebook_json = copy.deepcopy(notebook_json)
 
     cells = _get_cells(temp_file, len(notebook_info.temporary_lines), md=md)
@@ -208,7 +209,10 @@ def mutate(
 
     temp_notebook = os.path.join(os.path.dirname(temp_file), os.path.basename(notebook))
     with open(temp_notebook, "w", encoding="utf-8") as handle:
-        handle.write(f"{json.dumps(notebook_json, indent=1, ensure_ascii=False)}\n")
+        if notebook_txt.endswith("\n"):
+            handle.write(f"{json.dumps(notebook_json, indent=1, ensure_ascii=False)}\n")
+        else:
+            handle.write(f"{json.dumps(notebook_json, indent=1, ensure_ascii=False)}")
     move(temp_notebook, notebook)
     return True
 

tests/data/notebook_for_testing.ipynb

@@ -139,4 +139,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 4
-}
+}