Fixing pytest cases per request from mroeschke. Switching whatsnew version per request from mroeschke.

Author: SFuller4

doc/source/whatsnew/v1.5.0.rst

@@ -333,7 +333,6 @@ Other enhancements
 - :meth:`DataFrame.set_index` now supports a ``copy`` keyword. If ``False``, the underlying data is not copied when a new :class:`DataFrame` is returned (:issue:`48043`)
 - The method :meth:`.ExtensionArray.factorize` accepts ``use_na_sentinel=False`` for determining how null values are to be treated (:issue:`46601`)
 - The ``Dockerfile`` now installs a dedicated ``pandas-dev`` virtual environment for pandas development instead of using the ``base`` environment (:issue:`48427`)
-- :meth:`DataFrame.to_json` now supports a ``mode`` keyword with supported inputs 'w' and 'a'. Defaulting to 'w', 'a' can be used when lines=True and orient='records' to append record oriented json lines to an existing json file. (:issue:`35849`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_150.notable_bug_fixes:

doc/source/whatsnew/v1.6.0.rst

@@ -31,7 +31,7 @@ Other enhancements
 - :meth:`.GroupBy.quantile` now preserving nullable dtypes instead of casting to numpy dtypes (:issue:`37493`)
 - :meth:`Series.add_suffix`, :meth:`DataFrame.add_suffix`, :meth:`Series.add_prefix` and :meth:`DataFrame.add_prefix` support an ``axis`` argument. If ``axis`` is set, the default behaviour of which axis to consider can be overwritten (:issue:`47819`)
 - :func:`assert_frame_equal` now shows the first element where the DataFrames differ, analogously to ``pytest``'s output (:issue:`47910`)
--
+- :meth:`DataFrame.to_json` now supports a ``mode`` keyword with supported inputs 'w' and 'a'. Defaulting to 'w', 'a' can be used when lines=True and orient='records' to append record oriented json lines to an existing json file. (:issue:`35849`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_160.notable_bug_fixes:

pandas/tests/io/json/test_readlines.py

@@ -330,22 +330,20 @@ def test_to_json_append_mode(mode_):
     # Test ValueError when mode is not supported option
     df = DataFrame({"col1": [1, 2], "col2": ["a", "b"]})
     msg = (
-        f"mode={repr(mode_)} is not a valid option."
+        f"mode={mode_} is not a valid option."
         "Only 'w' and 'a' are currently supported."
     )
     with pytest.raises(ValueError, match=msg):
         df.to_json(mode=mode_, lines=False, orient="records")
 
 
-def to_json_append_output():
+def to_json_append_output_consistent_columns():
     # GH 35849
-    # Testing that resulting outputs read in as expected.
+    # Testing that resulting output reads in as expected.
+    # Testing same columns, new rows
     df1 = DataFrame({"col1": [1, 2], "col2": ["a", "b"]})
     df2 = DataFrame({"col1": [3, 4], "col2": ["c", "d"]})
-    df3 = DataFrame({"col2": ["e", "f"], "col3": ["!", "#"]})
-    df4 = DataFrame({"col4": [True, False]})
 
-    # Test 1, df1 and df2
     expected = DataFrame({"col1": [1, 2, 3, 4], "col2": ["a", "b", "c", "d"]})
     with tm.ensure_clean("test.json") as path:
         # Save dataframes to the same file
@@ -356,7 +354,46 @@ def to_json_append_output():
         result = read_json(path, lines=True)
         tm.assert_frame_equal(result, expected)
 
+
+def to_json_append_output_inconsistent_columns():
+    # GH 35849
+    # Testing that resulting output reads in as expected.
+    # Testing one new column, one old column, new rows
+    df1 = DataFrame({"col1": [1, 2], "col2": ["a", "b"]})
+    df3 = DataFrame({"col2": ["e", "f"], "col3": ["!", "#"]})
+
     # Test 2: df1, df2, df3, df4 (in that order)
+    expected = DataFrame(
+        {
+            "col1": [
+                1,
+                2,
+                None,
+                None,
+            ],
+            "col2": ["a", "b", "e", "f"],
+            "col3": [None, None, "!", "#"],
+        }
+    )
+    with tm.ensure_clean("test.json") as path:
+        # Save dataframes to the same file
+        df1.to_json(path, mode="a", lines=True, orient="records")
+        df3.to_json(path, mode="a", lines=True, orient="records")
+
+        # Read path file
+        result = read_json(path, lines=True)
+        tm.assert_frame_equal(result, expected)
+
+
+def to_json_append_output_different_columns():
+    # GH 35849
+    # Testing that resulting output reads in as expected.
+    # Testing same, differing and new columns
+    df1 = DataFrame({"col1": [1, 2], "col2": ["a", "b"]})
+    df2 = DataFrame({"col1": [3, 4], "col2": ["c", "d"]})
+    df3 = DataFrame({"col2": ["e", "f"], "col3": ["!", "#"]})
+    df4 = DataFrame({"col4": [True, False]})
+
     expected = DataFrame(
         {
             "col1": [1, 2, 3, 4, None, None, None, None],
@@ -376,7 +413,17 @@ def to_json_append_output():
         result = read_json(path, lines=True)
         tm.assert_frame_equal(result, expected)
 
-    # Test 3: df4, df3, df2, df1 (in that order)
+
+def to_json_append_output_different_columns_reordered():
+    # GH 35849
+    # Testing that resulting output reads in as expected.
+    # Testing specific result column order.
+    df1 = DataFrame({"col1": [1, 2], "col2": ["a", "b"]})
+    df2 = DataFrame({"col1": [3, 4], "col2": ["c", "d"]})
+    df3 = DataFrame({"col2": ["e", "f"], "col3": ["!", "#"]})
+    df4 = DataFrame({"col4": [True, False]})
+
+    # df4, df3, df2, df1 (in that order)
     expected = DataFrame(
         {
             "col4": [True, False, None, None, None, None, None, None],