ARROW-8416: [Python] Add feather alias for ipc format in dataset API

Closes #6919 from jorisvandenbossche/ARROW-8416

Authored-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Signed-off-by: Benjamin Kietzman <bengilgit@gmail.com>

python/pyarrow/dataset.py

@@ -226,7 +226,7 @@ def _ensure_format(obj):
         return obj
     elif obj == "parquet":
         return ParquetFileFormat()
-    elif obj == "ipc":
+    elif obj in {"ipc", "arrow", "feather"}:
         return IpcFileFormat()
     else:
         raise ValueError("format '{}' is not supported".format(obj))
@@ -326,7 +326,8 @@ def dataset(paths_or_factories, filesystem=None, partitioning=None,
         function. A flavor string can be used as shortcut, and with a list of
         field names a DirectionaryPartitioning will be inferred.
     format : str
-        Currently only "parquet" is supported.
+        Currently "parquet" and "ipc"/"arrow"/"feather" are supported. For
+        Feather, only version 2 files are supported.
     schema : Schema, optional
         Optionally provide the Schema for the Dataset, in which case it will
         not be inferred from the source.

python/pyarrow/tests/test_dataset.py

@@ -1234,6 +1234,31 @@ def test_ipc_format(tempdir):
     result = dataset.to_table()
     assert result.equals(table)
 
-    dataset = ds.dataset(path, format="ipc")
+    for format_str in ["ipc", "arrow"]:
+        dataset = ds.dataset(path, format=format_str)
+        result = dataset.to_table()
+        assert result.equals(table)
+
+
+def test_feather_format(tempdir):
+    from pyarrow.feather import write_feather
+
+    table = pa.table({'a': pa.array([1, 2, 3], type="int8"),
+                      'b': pa.array([.1, .2, .3], type="float64")})
+
+    basedir = tempdir / "feather_dataset"
+    basedir.mkdir()
+    write_feather(table, str(basedir / "data.feather"))
+
+    dataset = ds.dataset(basedir, format=ds.IpcFileFormat())
     result = dataset.to_table()
     assert result.equals(table)
+
+    dataset = ds.dataset(basedir, format="feather")
+    result = dataset.to_table()
+    assert result.equals(table)
+
+    # error with Feather v1 files
+    write_feather(table, str(basedir / "data1.feather"), version=1)
+    with pytest.raises(ValueError):
+        ds.dataset(basedir, format="feather").to_table()