Repository: pandas-dev/pandas (python)

Issue:
BUG:  pandas.read_parquet () dtype_backend argument does not get the default value as documented
### Pandas version checks

- [X] I have checked that this issue has not already been reported.

- [X] I have confirmed this bug exists on the [latest version](https://pandas.pydata.org/docs/whatsnew/index.html) of pandas.

- [ ] I have confirmed this bug exists on the [main branch](https://pandas.pydata.org/docs/dev/getting_started/install.html#installing-the-development-version-of-pandas) of pandas.


### Reproducible Example

```python
import pandas as pd
import pyarrow as pa
import pyarrow.parquet as pq

fields = [
    pa.field('int_column',pa.int32()),
    pa.field('float_column', pa.float32()),
    pa.field('bool_column', pa.bool_()),
]
schema = pa.schema(fields)
data = {'int_column': [1, 2, None, 4],
        'float_column': [1.5, 2.5, 3.5, None],
        'bool_column': [True, True, None, False]}
pa_table = pa.table(raw_data, schema=schema)
pq.write_table(pa_table, './example_table.parquet')

df1 = pd.read_parquet('./example_table.parquet')
df2 = pd.read_parquet('./example_table.parquet', dtype_backend='numpy_nullable')

print(df1.dtypes)
print(df2.dtypes)
```


### Issue Description

According to the documentation of `pd.read_parquet()`, the default value for `dtype_backend` is `'numpy_nullable'`.
Data types differ when not passing any argument from when passing `'numpy_nullable'`.
Specifically, if not passing any argument the data types are the not nullable ones.

### Expected Behavior

not passing an argument should give the same result as passing the default value.

### Installed Versions

<details>

NSTALLED VERSIONS
------------------
commit                : d9cdd2ee5a58015ef6f4d15c7226110c9aab8140
python                : 3.12.4.final.0
python-bits           : 64
OS                    : Linux
OS-release            : 6.8.0-38-generic
Version               : #38-Ubuntu SMP PREEMPT_DYNAMIC Fri Jun  7 15:25:01 UTC 2024
machine               : x86_64
processor             : x86_64
byteorder             : little
LC_ALL                : None
LANG                  : en_US.UTF-8
LOCALE                : en_US.UTF-8

pandas                : 2.2.2
numpy                 : 1.26.4
pytz                  : 2024.1
dateutil              : 2.9.0.post0
setuptools            : 69.5.1
pip                   : 24.0
Cython                : None
pytest                : 7.4.4
hypothesis            : None
sphinx                : 7.3.7
blosc                 : None
feather               : None
xlsxwriter            : None
lxml.etree            : 5.2.1
html5lib              : None
pymysql               : None
psycopg2              : None
jinja2                : 3.1.4
IPython               : 8.25.0
pandas_datareader     : None
adbc-driver-postgresql: None
adbc-driver-sqlite    : None
bs4                   : 4.12.3
bottleneck            : 1.3.7
dataframe-api-compat  : None
fastparquet           : None
fsspec                : 2024.3.1
gcsfs                 : None
matplotlib            : 3.8.4
numba                 : 0.59.1
numexpr               : 2.8.7
odfpy                 : None
openpyxl              : 3.1.2
pandas_gbq            : None
pyarrow               : 17.0.0
pyreadstat            : None
python-calamine       : None
pyxlsb                : None
s3fs                  : 2024.3.1
scipy                 : 1.13.1
sqlalchemy            : 2.0.30
tables                : 3.9.2
tabulate              : 0.9.0
xarray                : 2023.6.0
xlrd                  : None
zstandard             : 0.22.0
tzdata                : 2023.3
qtpy                  : 2.4.1
pyqt5                 : None

</details>


Pull request description:
DOC: More doc fix for dtype_backend
- [ ] Fix all changed in #54104, following #59021 
- [ ] Closes #59332
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.



Patch:
diff --git a/doc/source/whatsnew/v3.0.0.rst b/doc/source/whatsnew/v3.0.0.rst
index f95314b40d..ee9d18d0c7 100644
--- a/doc/source/whatsnew/v3.0.0.rst
+++ b/doc/source/whatsnew/v3.0.0.rst
@@ -50,6 +50,7 @@ Other enhancements
 - :meth:`DataFrame.pivot_table` and :func:`pivot_table` now allow the passing of keyword arguments to ``aggfunc`` through ``**kwargs`` (:issue:`57884`)
 - :meth:`Series.cummin` and :meth:`Series.cummax` now supports :class:`CategoricalDtype` (:issue:`52335`)
 - :meth:`Series.plot` now correctly handle the ``ylabel`` parameter for pie charts, allowing for explicit control over the y-axis label (:issue:`58239`)
+- :meth:`pandas.concat` will raise a ``ValueError`` when ``ignore_index=True`` and ``keys`` is not ``None`` (:issue:`59274`)
 - Multiplying two :class:`DateOffset` objects will now raise a ``TypeError`` instead of a ``RecursionError`` (:issue:`59442`)
 - Restore support for reading Stata 104-format and enable reading 103-format dta files (:issue:`58554`)
 - Support reading Stata 102-format (Stata 1) dta files (:issue:`58978`)
diff --git a/pandas/_libs/tslibs/nattype.pyx b/pandas/_libs/tslibs/nattype.pyx
index 130e41e510..81b59578fe 100644
--- a/pandas/_libs/tslibs/nattype.pyx
+++ b/pandas/_libs/tslibs/nattype.pyx
@@ -1047,7 +1047,7 @@ class NaTType(_NaT):
             * 'NaT' will return NaT for an ambiguous time.
             * 'raise' will raise an AmbiguousTimeError for an ambiguous time.
 
-        nonexistent : {'raise', 'shift_forward', 'shift_backward, 'NaT', \
+        nonexistent : {'raise', 'shift_forward', 'shift_backward', 'NaT', \
 timedelta}, default 'raise'
             A nonexistent time does not exist in a particular timezone
             where clocks moved forward due to DST.
@@ -1148,7 +1148,7 @@ timedelta}, default 'raise'
             * 'NaT' will return NaT for an ambiguous time.
             * 'raise' will raise an AmbiguousTimeError for an ambiguous time.
 
-        nonexistent : {'raise', 'shift_forward', 'shift_backward, 'NaT', \
+        nonexistent : {'raise', 'shift_forward', 'shift_backward', 'NaT', \
 timedelta}, default 'raise'
             A nonexistent time does not exist in a particular timezone
             where clocks moved forward due to DST.
@@ -1243,7 +1243,7 @@ timedelta}, default 'raise'
             * 'NaT' will return NaT for an ambiguous time.
             * 'raise' will raise an AmbiguousTimeError for an ambiguous time.
 
-        nonexistent : {'raise', 'shift_forward', 'shift_backward, 'NaT', \
+        nonexistent : {'raise', 'shift_forward', 'shift_backward', 'NaT', \
 timedelta}, default 'raise'
             A nonexistent time does not exist in a particular timezone
             where clocks moved forward due to DST.
@@ -1407,7 +1407,7 @@ timedelta}, default 'raise'
             * 'NaT' will return NaT for an ambiguous time.
             * 'raise' will raise an AmbiguousTimeError for an ambiguous time.
 
-        nonexistent : 'shift_forward', 'shift_backward, 'NaT', timedelta, \
+        nonexistent : 'shift_forward', 'shift_backward', 'NaT', timedelta, \
 default 'raise'
             A nonexistent time does not exist in a particular timezone
             where clocks moved forward due to DST.
diff --git a/pandas/_libs/tslibs/timestamps.pyx b/pandas/_libs/tslibs/timestamps.pyx
index 369184d9df..6779c8e7f4 100644
--- a/pandas/_libs/tslibs/timestamps.pyx
+++ b/pandas/_libs/tslibs/timestamps.pyx
@@ -2106,7 +2106,7 @@ class Timestamp(_Timestamp):
             * 'NaT' will return NaT for an ambiguous time.
             * 'raise' will raise an AmbiguousTimeError for an ambiguous time.
 
-        nonexistent : {'raise', 'shift_forward', 'shift_backward, 'NaT', \
+        nonexistent : {'raise', 'shift_forward', 'shift_backward', 'NaT', \
 timedelta}, default 'raise'
             A nonexistent time does not exist in a particular timezone
             where clocks moved forward due to DST.
@@ -2209,7 +2209,7 @@ timedelta}, default 'raise'
             * 'NaT' will return NaT for an ambiguous time.
             * 'raise' will raise an AmbiguousTimeError for an ambiguous time.
 
-        nonexistent : {'raise', 'shift_forward', 'shift_backward, 'NaT', \
+        nonexistent : {'raise', 'shift_forward', 'shift_backward', 'NaT', \
 timedelta}, default 'raise'
             A nonexistent time does not exist in a particular timezone
             where clocks moved forward due to DST.
@@ -2304,7 +2304,7 @@ timedelta}, default 'raise'
             * 'NaT' will return NaT for an ambiguous time.
             * 'raise' will raise an AmbiguousTimeError for an ambiguous time.
 
-        nonexistent : {'raise', 'shift_forward', 'shift_backward, 'NaT', \
+        nonexistent : {'raise', 'shift_forward', 'shift_backward', 'NaT', \
 timedelta}, default 'raise'
             A nonexistent time does not exist in a particular timezone
             where clocks moved forward due to DST.
@@ -2443,7 +2443,7 @@ timedelta}, default 'raise'
             * 'NaT' will return NaT for an ambiguous time.
             * 'raise' will raise an AmbiguousTimeError for an ambiguous time.
 
-        nonexistent : 'shift_forward', 'shift_backward, 'NaT', timedelta, \
+        nonexistent : 'shift_forward', 'shift_backward', 'NaT', timedelta, \
 default 'raise'
             A nonexistent time does not exist in a particular timezone
             where clocks moved forward due to DST.
diff --git a/pandas/core/dtypes/cast.py b/pandas/core/dtypes/cast.py
index 162f6a4d30..2107277b1c 100644
--- a/pandas/core/dtypes/cast.py
+++ b/pandas/core/dtypes/cast.py
@@ -1014,10 +1014,8 @@ def convert_dtypes(
         Back-end data type applied to the resultant :class:`DataFrame`
         (still experimental). Behaviour is as follows:
 
-        * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
+        * ``"numpy_nullable"``: returns nullable-dtype
         * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
 
         .. versionadded:: 2.0
 
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 8a6fc69d47..a585a967ab 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -6670,10 +6670,10 @@ class NDFrame(PandasObject, indexing.IndexingMixin):
             Back-end data type applied to the resultant :class:`DataFrame` or
             :class:`Series` (still experimental). Behaviour is as follows:
 
-            * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-              or :class:`Series` (default).
+            * ``"numpy_nullable"``: returns nullable-dtype-backed
+              :class:`DataFrame` or :class:`Serires`.
             * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-              DataFrame or Series.
+              :class:`DataFrame` or :class:`Series`.
 
             .. versionadded:: 2.0
 
diff --git a/pandas/core/reshape/concat.py b/pandas/core/reshape/concat.py
index 6836ba3f65..c005a1ce26 100644
--- a/pandas/core/reshape/concat.py
+++ b/pandas/core/reshape/concat.py
@@ -379,6 +379,11 @@ def concat(
     0   1   2
     1   3   4
     """
+    if ignore_index and keys is not None:
+        raise ValueError(
+            f"Cannot set {ignore_index=} and specify keys. Either should be used."
+        )
+
     if copy is not lib.no_default:
         warnings.warn(
             "The copy keyword is deprecated and will be removed in a future "
diff --git a/pandas/core/tools/numeric.py b/pandas/core/tools/numeric.py
index 26e73794af..982851d055 100644
--- a/pandas/core/tools/numeric.py
+++ b/pandas/core/tools/numeric.py
@@ -99,8 +99,8 @@ def to_numeric(
         is to not use nullable data types. If specified, the behavior
         is as follows:
 
-        * ``"numpy_nullable"``: returns with nullable-dtype-backed
-        * ``"pyarrow"``: returns with pyarrow-backed nullable :class:`ArrowDtype`
+        * ``"numpy_nullable"``: returns nullable-dtype-backed object
+        * ``"pyarrow"``: returns with pyarrow-backed nullable object
 
         .. versionadded:: 2.0
 
diff --git a/pandas/io/clipboards.py b/pandas/io/clipboards.py
index 5a0a8c321e..2ed241f0b9 100644
--- a/pandas/io/clipboards.py
+++ b/pandas/io/clipboards.py
@@ -38,14 +38,15 @@ def read_clipboard(
         A string or regex delimiter. The default of ``'\\s+'`` denotes
         one or more whitespace characters.
 
-    dtype_backend : {'numpy_nullable', 'pyarrow'}, default 'numpy_nullable'
+    dtype_backend : {'numpy_nullable', 'pyarrow'}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 
diff --git a/pandas/io/excel/_base.py b/pandas/io/excel/_base.py
index f83f9cb1c8..ef52107c28 100644
--- a/pandas/io/excel/_base.py
+++ b/pandas/io/excel/_base.py
@@ -267,14 +267,15 @@ skipfooter : int, default 0
     Rows at the end to skip (0-indexed).
 {storage_options}
 
-dtype_backend : {{'numpy_nullable', 'pyarrow'}}, default 'numpy_nullable'
+dtype_backend : {{'numpy_nullable', 'pyarrow'}}
     Back-end data type applied to the resultant :class:`DataFrame`
-    (still experimental). Behaviour is as follows:
+    (still experimental). If not specified, the default behavior
+    is to not use nullable data types. If specified, the behavior
+    is as follows:
 
     * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-      (default).
-    * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-      DataFrame.
+    * ``"pyarrow"``: returns pyarrow-backed nullable
+      :class:`ArrowDtype` :class:`DataFrame`
 
     .. versionadded:: 2.0
 
@@ -1728,14 +1729,15 @@ class ExcelFile:
             comment string and the end of the current line is ignored.
         skipfooter : int, default 0
             Rows at the end to skip (0-indexed).
-        dtype_backend : {{'numpy_nullable', 'pyarrow'}}, default 'numpy_nullable'
+        dtype_backend : {{'numpy_nullable', 'pyarrow'}}
             Back-end data type applied to the resultant :class:`DataFrame`
-            (still experimental). Behaviour is as follows:
+            (still experimental). If not specified, the default behavior
+            is to not use nullable data types. If specified, the behavior
+            is as follows:
 
             * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-              (default).
-            * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-              DataFrame.
+            * ``"pyarrow"``: returns pyarrow-backed nullable
+              :class:`ArrowDtype` :class:`DataFrame`
 
             .. versionadded:: 2.0
         **kwds : dict, optional
diff --git a/pandas/io/feather_format.py b/pandas/io/feather_format.py
index 3df3e77a85..aaae9857b4 100644
--- a/pandas/io/feather_format.py
+++ b/pandas/io/feather_format.py
@@ -92,14 +92,15 @@ def read_feather(
         Whether to parallelize reading using multiple threads.
     {storage_options}
 
-    dtype_backend : {{'numpy_nullable', 'pyarrow'}}, default 'numpy_nullable'
+    dtype_backend : {{'numpy_nullable', 'pyarrow'}}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
-        * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 
diff --git a/pandas/io/html.py b/pandas/io/html.py
index 4b8bc48130..c9897f628f 100644
--- a/pandas/io/html.py
+++ b/pandas/io/html.py
@@ -1131,14 +1131,15 @@ def read_html(
 
         .. versionadded:: 1.5.0
 
-    dtype_backend : {{'numpy_nullable', 'pyarrow'}}, default 'numpy_nullable'
+    dtype_backend : {{'numpy_nullable', 'pyarrow'}}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 
diff --git a/pandas/io/json/_json.py b/pandas/io/json/_json.py
index b29ead1d14..d077b9e0c4 100644
--- a/pandas/io/json/_json.py
+++ b/pandas/io/json/_json.py
@@ -652,14 +652,15 @@ def read_json(
 
     {storage_options}
 
-    dtype_backend : {{'numpy_nullable', 'pyarrow'}}, default 'numpy_nullable'
+    dtype_backend : {{'numpy_nullable', 'pyarrow'}}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 
diff --git a/pandas/io/orc.py b/pandas/io/orc.py
index b297164d5d..f179dafc91 100644
--- a/pandas/io/orc.py
+++ b/pandas/io/orc.py
@@ -61,14 +61,15 @@ def read_orc(
         Output always follows the ordering of the file and not the columns list.
         This mirrors the original behaviour of
         :external+pyarrow:py:meth:`pyarrow.orc.ORCFile.read`.
-    dtype_backend : {'numpy_nullable', 'pyarrow'}, default 'numpy_nullable'
+    dtype_backend : {'numpy_nullable', 'pyarrow'}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 
diff --git a/pandas/io/parquet.py b/pandas/io/parquet.py
index 77a9cc3fca..24415299e7 100644
--- a/pandas/io/parquet.py
+++ b/pandas/io/parquet.py
@@ -542,14 +542,15 @@ def read_parquet(
 
         .. versionadded:: 1.3.0
 
-    dtype_backend : {{'numpy_nullable', 'pyarrow'}}, default 'numpy_nullable'
+    dtype_backend : {{'numpy_nullable', 'pyarrow'}}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 
diff --git a/pandas/io/parsers/readers.py b/pandas/io/parsers/readers.py
index 0cca1ebdb8..b77c6a1c03 100644
--- a/pandas/io/parsers/readers.py
+++ b/pandas/io/parsers/readers.py
@@ -438,14 +438,14 @@ float_precision : {{'high', 'legacy', 'round_trip'}}, optional
 
 {storage_options}
 
-dtype_backend : {{'numpy_nullable', 'pyarrow'}}, default 'numpy_nullable'
+dtype_backend : {{'numpy_nullable', 'pyarrow'}}
     Back-end data type applied to the resultant :class:`DataFrame`
-    (still experimental). Behaviour is as follows:
+    (still experimental). If not specified, the default behavior
+    is to not use nullable data types. If specified, the behavior
+    is as follows:
 
     * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-      (default).
-    * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-      DataFrame.
+    * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype` :class:`DataFrame`
 
     .. versionadded:: 2.0
 
diff --git a/pandas/io/spss.py b/pandas/io/spss.py
index 313ffa79cb..e597463aee 100644
--- a/pandas/io/spss.py
+++ b/pandas/io/spss.py
@@ -36,14 +36,15 @@ def read_spss(
         Return a subset of the columns. If None, return all columns.
     convert_categoricals : bool, default is True
         Convert categorical columns into pd.Categorical.
-    dtype_backend : {'numpy_nullable', 'pyarrow'}, default 'numpy_nullable'
+    dtype_backend : {'numpy_nullable', 'pyarrow'}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed
+          nullable :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 
diff --git a/pandas/io/sql.py b/pandas/io/sql.py
index 4fd7de7a28..99dd06568f 100644
--- a/pandas/io/sql.py
+++ b/pandas/io/sql.py
@@ -306,14 +306,15 @@ def read_sql_table(
     chunksize : int, default None
         If specified, returns an iterator where `chunksize` is the number of
         rows to include in each chunk.
-    dtype_backend : {'numpy_nullable', 'pyarrow'}, default 'numpy_nullable'
+    dtype_backend : {'numpy_nullable', 'pyarrow'}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 
@@ -443,14 +444,15 @@ def read_sql_query(
         {'a': np.float64, 'b': np.int32, 'c': 'Int64'}.
 
         .. versionadded:: 1.3.0
-    dtype_backend : {'numpy_nullable', 'pyarrow'}, default 'numpy_nullable'
+    dtype_backend : {'numpy_nullable', 'pyarrow'}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 
@@ -586,14 +588,15 @@ def read_sql(
     chunksize : int, default None
         If specified, return an iterator where `chunksize` is the
         number of rows to include in each chunk.
-    dtype_backend : {'numpy_nullable', 'pyarrow'}, default 'numpy_nullable'
+    dtype_backend : {'numpy_nullable', 'pyarrow'}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
     dtype : Type name or dict of columns
@@ -1683,14 +1686,15 @@ class SQLDatabase(PandasSQL):
         chunksize : int, default None
             If specified, return an iterator where `chunksize` is the number
             of rows to include in each chunk.
-        dtype_backend : {'numpy_nullable', 'pyarrow'}, default 'numpy_nullable'
+        dtype_backend : {'numpy_nullable', 'pyarrow'}
             Back-end data type applied to the resultant :class:`DataFrame`
-            (still experimental). Behaviour is as follows:
+            (still experimental). If not specified, the default behavior
+            is to not use nullable data types. If specified, the behavior
+            is as follows:
 
             * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-              (default).
-            * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-              DataFrame.
+            * ``"pyarrow"``: returns pyarrow-backed nullable
+              :class:`ArrowDtype` :class:`DataFrame`
 
             .. versionadded:: 2.0
 
@@ -2148,14 +2152,15 @@ class ADBCDatabase(PandasSQL):
             schema of the SQL database object.
         chunksize : int, default None
             Raises NotImplementedError
-        dtype_backend : {'numpy_nullable', 'pyarrow'}, default 'numpy_nullable'
+        dtype_backend : {'numpy_nullable', 'pyarrow'}
             Back-end data type applied to the resultant :class:`DataFrame`
-            (still experimental). Behaviour is as follows:
+            (still experimental). If not specified, the default behavior
+            is to not use nullable data types. If specified, the behavior
+            is as follows:
 
             * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-              (default).
-            * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-              DataFrame.
+            * ``"pyarrow"``: returns pyarrow-backed nullable
+              :class:`ArrowDtype` :class:`DataFrame`
 
             .. versionadded:: 2.0
 
diff --git a/pandas/io/xml.py b/pandas/io/xml.py
index 8c7381a926..0fcf27af42 100644
--- a/pandas/io/xml.py
+++ b/pandas/io/xml.py
@@ -959,14 +959,15 @@ def read_xml(
 
     {storage_options}
 
-    dtype_backend : {{'numpy_nullable', 'pyarrow'}}, default 'numpy_nullable'
+    dtype_backend : {{'numpy_nullable', 'pyarrow'}}
         Back-end data type applied to the resultant :class:`DataFrame`
-        (still experimental). Behaviour is as follows:
+        (still experimental). If not specified, the default behavior
+        is to not use nullable data types. If specified, the behavior
+        is as follows:
 
         * ``"numpy_nullable"``: returns nullable-dtype-backed :class:`DataFrame`
-          (default).
-        * ``"pyarrow"``: returns pyarrow-backed nullable :class:`ArrowDtype`
-          DataFrame.
+        * ``"pyarrow"``: returns pyarrow-backed nullable
+          :class:`ArrowDtype` :class:`DataFrame`
 
         .. versionadded:: 2.0
 


Test patch:
diff --git a/pandas/tests/reshape/concat/test_concat.py b/pandas/tests/reshape/concat/test_concat.py
index b2caa1fadd..8af224f1ad 100644
--- a/pandas/tests/reshape/concat/test_concat.py
+++ b/pandas/tests/reshape/concat/test_concat.py
@@ -939,3 +939,14 @@ def test_concat_with_series_and_frame_returns_rangeindex_columns():
     result = concat([ser, df])
     expected = DataFrame([0, 1, 2], index=[0, 0, 1])
     tm.assert_frame_equal(result, expected, check_column_type=True)
+
+
+def test_concat_with_moot_ignore_index_and_keys():
+    df1 = DataFrame([[0]])
+    df2 = DataFrame([[42]])
+
+    ignore_index = True
+    keys = ["df1", "df2"]
+    msg = f"Cannot set {ignore_index=} and specify keys. Either should be used."
+    with pytest.raises(ValueError, match=msg):
+        concat([df1, df2], keys=keys, ignore_index=ignore_index)