DEPR: Deprecated passing arguments as positional in pd.concat (#41718)

Author: tegardp

doc/source/whatsnew/v0.17.0.rst

@@ -423,7 +423,7 @@ Other enhancements
 
   .. code-block:: ipython
 
-     In [1]: pd.concat([foo, bar, baz], 1)
+     In [1]: pd.concat([foo, bar, baz], axis=1)
      Out[1]:
            0  1  2
         0  1  1  4
@@ -433,7 +433,7 @@ Other enhancements
 
   .. ipython:: python
 
-    pd.concat([foo, bar, baz], 1)
+    pd.concat([foo, bar, baz], axis=1)
 
 - ``DataFrame`` has gained the ``nlargest`` and ``nsmallest`` methods (:issue:`10393`)
 

doc/source/whatsnew/v1.3.0.rst

@@ -711,6 +711,7 @@ Deprecations
 - Deprecated passing lists as ``key`` to :meth:`DataFrame.xs` and :meth:`Series.xs` (:issue:`41760`)
 - Deprecated passing arguments as positional in :meth:`DataFrame.drop` (other than ``"labels"``) and :meth:`Series.drop` (:issue:`41485`)
 - Deprecated passing arguments as positional (other than ``filepath_or_buffer``) in :func:`read_table` (:issue:`41485`)
+- Deprecated passing arguments as positional (other than ``objs``) in :func:`concat` (:issue:`41485`)
 
 
 .. _whatsnew_130.deprecations.nuisance_columns:

pandas/core/reshape/concat.py

@@ -16,7 +16,10 @@
 import numpy as np
 
 from pandas._typing import FrameOrSeriesUnion
-from pandas.util._decorators import cache_readonly
+from pandas.util._decorators import (
+    cache_readonly,
+    deprecate_nonkeyword_arguments,
+)
 
 from pandas.core.dtypes.concat import concat_compat
 from pandas.core.dtypes.generic import (
@@ -84,6 +87,7 @@ def concat(
     ...
 
 
+@deprecate_nonkeyword_arguments(version=None, allowed_args=["objs"])
 def concat(
     objs: Iterable[NDFrame] | Mapping[Hashable, NDFrame],
     axis=0,

pandas/io/stata.py

@@ -1762,7 +1762,7 @@ def _do_convert_missing(self, data: DataFrame, convert_missing: bool) -> DataFra
             columns = data.columns
             replacement_df = DataFrame(replacements)
             replaced = concat(
-                [data.drop(replacement_df.columns, axis=1), replacement_df], 1
+                [data.drop(replacement_df.columns, axis=1), replacement_df], axis=1
             )
             data = replaced[columns]
         return data

pandas/tests/io/pytables/test_complex.py

@@ -205,4 +205,4 @@ def test_complex_append(setup_path):
         store.append("df", df, data_columns=["b"])
         store.append("df", df)
         result = store.select("df")
-        tm.assert_frame_equal(pd.concat([df, df], 0), result)
+        tm.assert_frame_equal(pd.concat([df, df], axis=0), result)

pandas/tests/reshape/concat/test_concat.py

@@ -638,3 +638,18 @@ def test_concat_multiindex_with_empty_rangeindex():
     result = concat([df1, df2])
     expected = DataFrame([[1, 2], [np.nan, np.nan]], columns=mi)
     tm.assert_frame_equal(result, expected)
+
+
+def test_concat_posargs_deprecation():
+    # https://github.com/pandas-dev/pandas/issues/41485
+    df = DataFrame([[1, 2, 3]], index=["a"])
+    df2 = DataFrame([[4, 5, 6]], index=["b"])
+
+    msg = (
+        "In a future version of pandas all arguments of concat "
+        "except for the argument 'objs' will be keyword-only"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = concat([df, df2], 0)
+    expected = DataFrame([[1, 2, 3], [4, 5, 6]], index=["a", "b"])
+    tm.assert_frame_equal(result, expected)

pandas/tests/reshape/concat/test_invalid.py

@@ -27,13 +27,12 @@ def test_concat_invalid(self):
 
     def test_concat_invalid_first_argument(self):
         df1 = tm.makeCustomDataframe(10, 2)
-        df2 = tm.makeCustomDataframe(10, 2)
         msg = (
             "first argument must be an iterable of pandas "
             'objects, you passed an object of type "DataFrame"'
         )
         with pytest.raises(TypeError, match=msg):
-            concat(df1, df2)
+            concat(df1)
 
         # generator ok though
         concat(DataFrame(np.random.rand(5, 5)) for _ in range(3))