diff --git a/autotest/utilities/test_gdalalg_info.py b/autotest/utilities/test_gdalalg_info.py
index 94d493a67e7d..1f3d157ac4b0 100755
--- a/autotest/utilities/test_gdalalg_info.py
+++ b/autotest/utilities/test_gdalalg_info.py
@@ -17,8 +17,7 @@
 
 
 def get_info_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    return reg.InstantiateAlg("info")
+    return gdal.GetGlobalAlgorithmRegistry()["info"]
 
 
 @pytest.mark.parametrize(
@@ -31,7 +30,7 @@ def get_info_alg():
 def test_gdalalg_info_on_raster(args):
     info = get_info_alg()
     assert info.ParseRunAndFinalize(args)
-    output_string = info.GetActualAlgorithm().GetArg("output-string").Get()
+    output_string = info["output-string"]
     assert output_string.startswith("Driver: GTiff/GeoTIFF")
 
 
@@ -57,7 +56,7 @@ def test_gdalalg_info_on_raster_invalid_arg():
 def test_gdalalg_info_on_vector(args):
     info = get_info_alg()
     assert info.ParseRunAndFinalize(args)
-    output_string = info.GetActualAlgorithm().GetArg("output-string").Get()
+    output_string = info["output-string"]
     assert output_string.startswith("INFO: Open of")
 
 
@@ -75,8 +74,7 @@ def test_gdalalg_info_invalid_arg():
 
 def test_gdalalg_info_run_cannot_be_run():
     info = get_info_alg()
-    ds = gdal.GetDriverByName("MEM").Create("", 1, 1)
-    info.GetArg("input").SetDataset(ds)
+    info["input"] = gdal.GetDriverByName("MEM").Create("", 1, 1)
     with pytest.raises(Exception, match="method should not be called directly"):
         info.Run()
 
@@ -108,6 +106,6 @@ def test_gdalalg_info_mixed_raster_vector_with_invalid_arg(tmp_vsimem):
 def test_gdalalg_info_mixed_run_without_arg(tmp_vsimem):
 
     info = get_info_alg()
-    info.GetArg("input").Get().SetName("data/utmsmall.tif")
+    info["input"] = "data/utmsmall.tif"
     with pytest.raises(Exception, match="should not be called directly"):
         assert info.Run()
diff --git a/autotest/utilities/test_gdalalg_pipeline.py b/autotest/utilities/test_gdalalg_pipeline.py
index 6e3f80b898b4..5f0468b421ee 100755
--- a/autotest/utilities/test_gdalalg_pipeline.py
+++ b/autotest/utilities/test_gdalalg_pipeline.py
@@ -17,8 +17,7 @@
 
 
 def get_pipeline_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    return reg.InstantiateAlg("pipeline")
+    return gdal.GetGlobalAlgorithmRegistry()["pipeline"]
 
 
 def test_gdalalg_pipeline_read_and_write(tmp_vsimem):
@@ -44,6 +43,6 @@ def my_progress(pct, msg, user_data):
 def test_gdalalg_pipeline_mixed_run_without_arg(tmp_vsimem):
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("input").Get().SetDataset(gdal.OpenEx("../ogr/data/poly.shp"))
+    pipeline["input"] = gdal.OpenEx("../ogr/data/poly.shp")
     with pytest.raises(Exception, match="should not be called directly"):
         assert pipeline.Run()
diff --git a/autotest/utilities/test_gdalalg_raster_convert.py b/autotest/utilities/test_gdalalg_raster_convert.py
index a774972f1645..739ad35eebd0 100755
--- a/autotest/utilities/test_gdalalg_raster_convert.py
+++ b/autotest/utilities/test_gdalalg_raster_convert.py
@@ -53,7 +53,7 @@ def test_gdalalg_raster_convert_to_mem():
     convert = get_convert_alg()
     assert convert.ParseCommandLineArguments(["--of=MEM", "data/utmsmall.tif", ""])
     assert convert.Run()
-    out_ds = convert.GetArg("output").Get().GetDataset()
+    out_ds = convert["output"].GetDataset()
     assert out_ds.GetRasterBand(1).Checksum() == 50054
 
 
@@ -82,8 +82,7 @@ def test_gdalalg_raster_convert_append(tmp_vsimem):
 
 def test_gdalalg_raster_convert_error_output_already_set():
     convert = get_convert_alg()
-    ds = gdal.GetDriverByName("MEM").Create("", 1, 1)
-    convert.GetArg("output").Get().SetDataset(ds)
+    convert["output"] = gdal.GetDriverByName("MEM").Create("", 1, 1)
     assert convert.ParseCommandLineArguments(["data/utmsmall.tif"])
     with pytest.raises(
         Exception,
diff --git a/autotest/utilities/test_gdalalg_raster_edit.py b/autotest/utilities/test_gdalalg_raster_edit.py
index d85556a8f36a..0f24976fd4f9 100755
--- a/autotest/utilities/test_gdalalg_raster_edit.py
+++ b/autotest/utilities/test_gdalalg_raster_edit.py
@@ -17,9 +17,7 @@
 
 
 def get_edit_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    raster = reg.InstantiateAlg("raster")
-    return raster.InstantiateSubAlgorithm("edit")
+    return gdal.GetGlobalAlgorithmRegistry()["raster"]["edit"]
 
 
 def test_gdalalg_raster_edit_read_only(tmp_vsimem):
@@ -28,7 +26,7 @@ def test_gdalalg_raster_edit_read_only(tmp_vsimem):
     gdal.FileFromMemBuffer(tmp_filename, open("../gcore/data/byte.tif", "rb").read())
 
     pipeline = get_edit_alg()
-    pipeline.GetArg("dataset").Set(gdal.OpenEx(tmp_filename))
+    pipeline["dataset"] = gdal.OpenEx(tmp_filename)
     with pytest.raises(
         Exception, match="edit: Dataset should be opened in update mode"
     ):
diff --git a/autotest/utilities/test_gdalalg_raster_info.py b/autotest/utilities/test_gdalalg_raster_info.py
index 18a8857c9cd7..f4a10b88333c 100755
--- a/autotest/utilities/test_gdalalg_raster_info.py
+++ b/autotest/utilities/test_gdalalg_raster_info.py
@@ -19,9 +19,7 @@
 
 
 def get_info_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    raster = reg.InstantiateAlg("raster")
-    return raster.InstantiateSubAlgorithm("info")
+    return gdal.GetGlobalAlgorithmRegistry()["raster"]["info"]
 
 
 def test_gdalalg_raster_info_stdout():
@@ -41,7 +39,7 @@ def test_gdalalg_raster_info_stdout():
 def test_gdalalg_raster_info():
     info = get_info_alg()
     assert info.ParseRunAndFinalize(["--format=text", "data/utmsmall.tif"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     assert output_string.startswith("Driver: GTiff/GeoTIFF")
 
 
@@ -50,7 +48,7 @@ def test_gdalalg_raster_info_mm_checksum():
     assert info.ParseRunAndFinalize(
         ["--format=text", "--mm", "--checksum", "data/utmsmall.tif"]
     )
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     assert "   Computed Min/Max=0.000,255.000" in output_string
     assert "Checksum=" in output_string
 
@@ -58,9 +56,9 @@ def test_gdalalg_raster_info_mm_checksum():
 def test_gdalalg_raster_info_stats():
     info = get_info_alg()
     ds = gdal.Translate("", "../gcore/data/byte.tif", format="MEM")
-    info.GetArg("input").SetDataset(ds)
+    info["input"] = ds
     assert info.ParseRunAndFinalize(["--stats"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert "stdDev" in j["bands"][0]
 
@@ -68,9 +66,9 @@ def test_gdalalg_raster_info_stats():
 def test_gdalalg_raster_info_approx_stats():
     info = get_info_alg()
     ds = gdal.Translate("", "../gcore/data/byte.tif", format="MEM")
-    info.GetArg("input").SetDataset(ds)
+    info["input"] = ds
     assert info.ParseRunAndFinalize(["--approx-stats"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert "stdDev" in j["bands"][0]
 
@@ -78,9 +76,9 @@ def test_gdalalg_raster_info_approx_stats():
 def test_gdalalg_raster_info_hist():
     info = get_info_alg()
     ds = gdal.Translate("", "../gcore/data/byte.tif", format="MEM")
-    info.GetArg("input").SetDataset(ds)
+    info["input"] = ds
     assert info.ParseRunAndFinalize(["--hist"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert "histogram" in j["bands"][0]
 
@@ -88,7 +86,7 @@ def test_gdalalg_raster_info_hist():
 def test_gdalalg_raster_info_no_options():
     info = get_info_alg()
     ds = gdal.Translate("", "../gcore/data/byte.tif", format="MEM")
-    info.GetArg("input").SetDataset(ds)
+    info["input"] = ds
     assert info.ParseRunAndFinalize(
         ["--no-gcp", "--no-md", "--no-ct", "--no-fl", "--no-nodata", "--no-mask"]
     )
@@ -98,9 +96,9 @@ def test_gdalalg_raster_info_list_mdd():
     info = get_info_alg()
     ds = gdal.Translate("", "../gcore/data/byte.tif", format="MEM")
     ds.SetMetadataItem("foo", "bar", "MY_DOMAIN")
-    info.GetArg("input").SetDataset(ds)
+    info["input"] = ds
     assert info.ParseRunAndFinalize(["--list-mdd"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert "MY_DOMAIN" in j["metadata"]["metadataDomains"]
 
@@ -109,9 +107,9 @@ def test_gdalalg_raster_info_mdd_all():
     info = get_info_alg()
     ds = gdal.Translate("", "../gcore/data/byte.tif", format="MEM")
     ds.SetMetadataItem("foo", "bar", "MY_DOMAIN")
-    info.GetArg("input").SetDataset(ds)
+    info["input"] = ds
     assert info.ParseRunAndFinalize(["--mdd=all"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert j["metadata"] == {
         "": {"AREA_OR_POINT": "Area"},
@@ -128,7 +126,7 @@ def test_gdalalg_raster_info_list_subdataset():
     assert info.ParseRunAndFinalize(
         ["--input=../gcore/data/tiff_with_subifds.tif", "--subdataset=2"]
     )
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert j["description"] == "GTIFF_DIR:2:../gcore/data/tiff_with_subifds.tif"
 
@@ -149,7 +147,7 @@ def test_gdalalg_raster_info_list_subdataset_error_cannot_open_subdataset():
     ds = gdal.GetDriverByName("MEM").Create("", 1, 1)
     ds.SetMetadataItem("SUBDATASET_1_DESC", "desc", "SUBDATASETS")
     ds.SetMetadataItem("SUBDATASET_1_NAME", "i_do_not_exist", "SUBDATASETS")
-    info.GetArg("input").SetDataset(ds)
+    info["input"] = ds
     with pytest.raises(
         Exception,
         match="i_do_not_exist",
diff --git a/autotest/utilities/test_gdalalg_raster_mosaic.py b/autotest/utilities/test_gdalalg_raster_mosaic.py
index 414d871a9f07..4100b53aef3c 100755
--- a/autotest/utilities/test_gdalalg_raster_mosaic.py
+++ b/autotest/utilities/test_gdalalg_raster_mosaic.py
@@ -17,27 +17,23 @@
 
 
 def get_mosaic_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    raster = reg.InstantiateAlg("raster")
-    return raster.InstantiateSubAlgorithm("mosaic")
+    return gdal.GetGlobalAlgorithmRegistry()["raster"]["mosaic"]
 
 
 def test_gdalalg_raster_mosaic_from_dataset_handle():
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set(
-        [
-            gdal.Translate(
-                "", "../gcore/data/byte.tif", options="-f MEM -srcwin 0 0 10 20"
-            ),
-            gdal.Translate(
-                "", "../gcore/data/byte.tif", options="-f MEM -srcwin 10 0 10 20"
-            ),
-        ]
-    )
-    alg.GetArg("output").Set("")
+    alg["input"] = [
+        gdal.Translate(
+            "", "../gcore/data/byte.tif", options="-f MEM -srcwin 0 0 10 20"
+        ),
+        gdal.Translate(
+            "", "../gcore/data/byte.tif", options="-f MEM -srcwin 10 0 10 20"
+        ),
+    ]
+    alg["output"] = ""
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterXSize == 20
     assert ds.RasterYSize == 20
     assert ds.GetGeoTransform() == pytest.approx(
@@ -49,10 +45,10 @@ def test_gdalalg_raster_mosaic_from_dataset_handle():
 def test_gdalalg_raster_mosaic_from_dataset_name():
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set(["../gcore/data/byte.tif"])
-    alg.GetArg("output").Set("")
+    alg["input"] = ["../gcore/data/byte.tif"]
+    alg["output"] = ""
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterXSize == 20
     assert ds.RasterYSize == 20
     assert ds.GetGeoTransform() == pytest.approx(
@@ -97,7 +93,7 @@ def test_gdalalg_raster_mosaic_bbox():
         ]
     )
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterXSize == 18
     assert ds.RasterYSize == 18
     assert ds.GetGeoTransform() == pytest.approx(
@@ -114,11 +110,11 @@ def test_gdalalg_raster_mosaic_resolution_average():
     src2_ds.SetGeoTransform([3, 0.5, 0, 49, 0, -0.5])
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([src1_ds, src2_ds])
-    alg.GetArg("resolution").Set("average")
-    alg.GetArg("output").Set("")
+    alg["input"] = [src1_ds, src2_ds]
+    alg["resolution"] = "average"
+    alg["output"] = ""
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterXSize == 3
     assert ds.RasterYSize == 1
     assert ds.GetGeoTransform() == pytest.approx((2.0, 0.75, 0.0, 49.0, 0.0, -0.75))
@@ -132,11 +128,11 @@ def test_gdalalg_raster_mosaic_resolution_highest():
     src2_ds.SetGeoTransform([3, 0.5, 0, 49, 0, -0.5])
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([src1_ds, src2_ds])
-    alg.GetArg("output").Set("")
-    alg.GetArg("resolution").Set("highest")
+    alg["input"] = [src1_ds, src2_ds]
+    alg["output"] = ""
+    alg["resolution"] = "highest"
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterXSize == 4
     assert ds.RasterYSize == 2
     assert ds.GetGeoTransform() == pytest.approx((2.0, 0.5, 0.0, 49.0, 0.0, -0.5))
@@ -150,11 +146,11 @@ def test_gdalalg_raster_mosaic_resolution_lowest():
     src2_ds.SetGeoTransform([3, 0.5, 0, 49, 0, -0.5])
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([src1_ds, src2_ds])
-    alg.GetArg("output").Set("")
-    alg.GetArg("resolution").Set("lowest")
+    alg["input"] = [src1_ds, src2_ds]
+    alg["output"] = ""
+    alg["resolution"] = "lowest"
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterXSize == 2
     assert ds.RasterYSize == 1
     assert ds.GetGeoTransform() == pytest.approx((2.0, 1.0, 0.0, 49.0, 0.0, -1.0))
@@ -168,11 +164,11 @@ def test_gdalalg_raster_mosaic_resolution_custom():
     src2_ds.SetGeoTransform([3, 0.5, 0, 49, 0, -0.5])
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([src1_ds, src2_ds])
-    alg.GetArg("output").Set("")
-    alg.GetArg("resolution").Set("0.5,1")
+    alg["input"] = [src1_ds, src2_ds]
+    alg["output"] = ""
+    alg["resolution"] = "0.5,1"
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterXSize == 4
     assert ds.RasterYSize == 1
     assert ds.GetGeoTransform() == pytest.approx((2.0, 0.5, 0.0, 49.0, 0.0, -1.0))
@@ -186,12 +182,12 @@ def test_gdalalg_raster_mosaic_target_aligned_pixels():
     src2_ds.SetGeoTransform([3, 0.5, 0, 49, 0, -0.5])
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([src1_ds, src2_ds])
-    alg.GetArg("output").Set("")
-    alg.GetArg("resolution").Set("0.3,0.6")
-    alg.GetArg("target-aligned-pixels").Set(True)
+    alg["input"] = [src1_ds, src2_ds]
+    alg["output"] = ""
+    alg["resolution"] = "0.3,0.6"
+    alg["target-aligned-pixels"] = True
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterXSize == 8
     assert ds.RasterYSize == 2
     assert ds.GetGeoTransform() == pytest.approx((1.8, 0.3, 0.0, 49.2, 0.0, -0.6))
@@ -205,8 +201,8 @@ def test_gdalalg_raster_mosaic_resolution_same_default():
     src2_ds.SetGeoTransform([3, 0.5, 0, 49, 0, -0.5])
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([src1_ds, src2_ds])
-    alg.GetArg("output").Set("")
+    alg["input"] = [src1_ds, src2_ds]
+    alg["output"] = ""
     with pytest.raises(
         Exception,
         match="whereas previous sources have resolution",
@@ -221,19 +217,19 @@ def test_gdalalg_raster_mosaic_resolution_invalid():
         Exception,
         match="resolution: two comma separated positive values should be provided, or 'same', 'average', 'highest' or 'lowest'",
     ):
-        alg.GetArg("resolution").Set("invalid")
+        alg["resolution"] = "invalid"
 
     with pytest.raises(
         Exception,
         match="resolution: two comma separated positive values should be provided, or 'same', 'average', 'highest' or 'lowest'",
     ):
-        alg.GetArg("resolution").Set("0.5")
+        alg["resolution"] = "0.5"
 
     with pytest.raises(
         Exception,
         match="resolution: two comma separated positive values should be provided, or 'same', 'average', 'highest' or 'lowest'",
     ):
-        alg.GetArg("resolution").Set("-0.5,-0.5")
+        alg["resolution"] = "-0.5,-0.5"
 
 
 def test_gdalalg_raster_mosaic_srcnodata_dstnodata():
@@ -243,12 +239,12 @@ def test_gdalalg_raster_mosaic_srcnodata_dstnodata():
     src1_ds.GetRasterBand(1).Fill(1)
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([src1_ds])
-    alg.GetArg("output").Set("")
-    alg.GetArg("srcnodata").Set([1])
-    alg.GetArg("dstnodata").Set([2])
+    alg["input"] = [src1_ds]
+    alg["output"] = ""
+    alg["srcnodata"] = [1]
+    alg["dstnodata"] = [2]
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.GetRasterBand(1).Checksum() == 2
     assert ds.GetRasterBand(1).GetNoDataValue() == 2
 
@@ -260,13 +256,13 @@ def test_gdalalg_raster_mosaic_hidenodata():
     src1_ds.GetRasterBand(1).Fill(1)
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([src1_ds])
-    alg.GetArg("output").Set("")
-    alg.GetArg("srcnodata").Set([1])
-    alg.GetArg("dstnodata").Set([2])
-    alg.GetArg("hidenodata").Set(True)
+    alg["input"] = [src1_ds]
+    alg["output"] = ""
+    alg["srcnodata"] = [1]
+    alg["dstnodata"] = [2]
+    alg["hidenodata"] = True
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.GetRasterBand(1).Checksum() == 2
     assert ds.GetRasterBand(1).GetNoDataValue() is None
 
@@ -274,25 +270,11 @@ def test_gdalalg_raster_mosaic_hidenodata():
 def test_gdalalg_raster_mosaic_addalpha():
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set(["../gcore/data/byte.tif"])
-    alg.GetArg("output").Set("")
-    alg.GetArg("addalpha").Set(True)
-    assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
-    assert ds.RasterCount == 2
-    assert ds.GetRasterBand(1).Checksum() == 4672
-    assert ds.GetRasterBand(2).GetColorInterpretation() == gdal.GCI_AlphaBand
-    assert ds.GetRasterBand(2).Checksum() == 4873
-
-
-def test_gdalalg_raster_mosaic_band():
-
-    alg = get_mosaic_alg()
-    alg.GetArg("input").Set(["../gcore/data/rgbsmall.tif"])
-    alg.GetArg("output").Set("")
-    alg.GetArg("band").Set([3, 2])
+    alg["input"] = ["../gcore/data/rgbsmall.tif"]
+    alg["output"] = ""
+    alg["band"] = [3, 2]
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterCount == 2
     assert ds.GetRasterBand(1).Checksum() == 21349
     assert ds.GetRasterBand(2).Checksum() == 21053
@@ -301,10 +283,10 @@ def test_gdalalg_raster_mosaic_band():
 def test_gdalalg_raster_mosaic_glob():
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set(["../gcore/data/rgbsm?ll.tif"])
-    alg.GetArg("output").Set("")
+    alg["input"] = ["../gcore/data/rgbsm?ll.tif"]
+    alg["output"] = ""
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.RasterCount == 3
 
 
@@ -314,18 +296,18 @@ def test_gdalalg_raster_mosaic_at_filename(tmp_vsimem):
     gdal.FileFromMemBuffer(input_file_list, "../gcore/data/byte.tif")
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([f"@{input_file_list}"])
-    alg.GetArg("output").Set("")
+    alg["input"] = [f"@{input_file_list}"]
+    alg["output"] = ""
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.GetRasterBand(1).Checksum() == 4672
 
 
 def test_gdalalg_raster_mosaic_at_filename_error():
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set(["@i_do_not_exist"])
-    alg.GetArg("output").Set("")
+    alg["input"] = ["@i_do_not_exist"]
+    alg["output"] = ""
     with pytest.raises(Exception, match="mosaic: Cannot open i_do_not_exist"):
         alg.Run()
 
@@ -335,8 +317,8 @@ def test_gdalalg_raster_mosaic_output_ds_alread_set():
     out_ds = gdal.GetDriverByName("MEM").Create("", 1, 1)
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set(["../gcore/data/byte.tif"])
-    alg.GetArg("output").Set(out_ds)
+    alg["input"] = ["../gcore/data/byte.tif"]
+    alg["output"] = out_ds
     with pytest.raises(
         Exception,
         match="mosaic: gdal raster mosaic does not support outputting to an already opened output dataset",
@@ -347,11 +329,11 @@ def test_gdalalg_raster_mosaic_output_ds_alread_set():
 def test_gdalalg_raster_mosaic_co():
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set(["../gcore/data/byte.tif"])
-    alg.GetArg("output").Set("")
-    alg.GetArg("creation-option").Set(["BLOCKXSIZE=10", "BLOCKYSIZE=15"])
+    alg["input"] = ["../gcore/data/byte.tif"]
+    alg["output"] = ""
+    alg["creation-option"] = ["BLOCKXSIZE=10", "BLOCKYSIZE=15"]
     assert alg.Run()
-    ds = alg.GetArg("output").Get().GetDataset()
+    ds = alg["output"].GetDataset()
     assert ds.GetRasterBand(1).GetBlockSize() == [10, 15]
 
 
@@ -405,8 +387,8 @@ def test_gdalalg_raster_mosaic_inconsistent_characteristics():
     src2_ds.SetSpatialRef(srs)
 
     alg = get_mosaic_alg()
-    alg.GetArg("input").Set([src1_ds, src2_ds])
-    alg.GetArg("output").Set("")
+    alg["input"] = [src1_ds, src2_ds]
+    alg["output"] = ""
     with pytest.raises(
         Exception, match="gdal raster mosaic does not support heterogeneous projection"
     ):
diff --git a/autotest/utilities/test_gdalalg_raster_overview.py b/autotest/utilities/test_gdalalg_raster_overview.py
index e193469d5154..d911b480e661 100755
--- a/autotest/utilities/test_gdalalg_raster_overview.py
+++ b/autotest/utilities/test_gdalalg_raster_overview.py
@@ -17,28 +17,26 @@
 
 
 def get_overview_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    raster = reg.InstantiateAlg("raster")
-    return raster.InstantiateSubAlgorithm("overview")
+    return gdal.GetGlobalAlgorithmRegistry()["raster"]["overview"]
 
 
 def get_overview_add_alg():
-    return get_overview_alg().InstantiateSubAlgorithm("add")
+    return get_overview_alg()["add"]
 
 
 def get_overview_delete_alg():
-    return get_overview_alg().InstantiateSubAlgorithm("delete")
+    return get_overview_alg()["delete"]
 
 
 def test_gdalalg_overview_invalid_arguments():
 
     add = get_overview_add_alg()
     with pytest.raises(Exception):
-        add.GetArg("levels").Set([1])
+        add["levels"] = [1]
 
     add = get_overview_add_alg()
     with pytest.raises(Exception):
-        add.GetArg("min-size").Set(0)
+        add["min-size"] = 0
 
 
 def test_gdalalg_overview_explicit_level():
@@ -46,8 +44,8 @@ def test_gdalalg_overview_explicit_level():
     ds = gdal.Translate("", "../gcore/data/byte.tif", format="MEM")
 
     add = get_overview_add_alg()
-    add.GetArg("dataset").Get().SetDataset(ds)
-    add.GetArg("levels").Set([2])
+    add["dataset"] = ds
+    add["levels"] = [2]
     assert add.Run()
 
     assert ds.GetRasterBand(1).Checksum() == 4672
@@ -60,9 +58,9 @@ def test_gdalalg_overview_minsize_and_resampling():
     ds = gdal.Translate("", "../gcore/data/byte.tif", format="MEM")
 
     add = get_overview_add_alg()
-    add.GetArg("dataset").Get().SetDataset(ds)
-    add.GetArg("resampling").Set("average")
-    add.GetArg("min-size").Set(10)
+    add["dataset"] = ds
+    add["resampling"] = "average"
+    add["min-size"] = 10
     assert add.Run()
 
     assert ds.GetRasterBand(1).Checksum() == 4672
@@ -76,9 +74,9 @@ def test_gdalalg_overview_reuse_resampling_and_levels(tmp_vsimem):
     ds = gdal.Translate(tmp_filename, "../gcore/data/byte.tif")
 
     add = get_overview_add_alg()
-    add.GetArg("dataset").Get().SetDataset(ds)
-    add.GetArg("resampling").Set("average")
-    add.GetArg("min-size").Set(10)
+    add["dataset"] = ds
+    add["resampling"] = "average"
+    add["min-size"] = 10
     assert add.Run()
 
     assert ds.GetRasterBand(1).Checksum() == 4672
@@ -89,7 +87,7 @@ def test_gdalalg_overview_reuse_resampling_and_levels(tmp_vsimem):
     ds.GetRasterBand(1).GetOverview(0).Fill(0)
 
     add = get_overview_add_alg()
-    add.GetArg("dataset").Get().SetDataset(ds)
+    add["dataset"] = ds
     assert add.Run()
 
     assert ds.GetRasterBand(1).Checksum() == 4672
@@ -136,15 +134,15 @@ def test_gdalalg_overview_delete():
     ds = gdal.Translate("", "../gcore/data/byte.tif", format="MEM")
 
     add = get_overview_add_alg()
-    add.GetArg("dataset").Get().SetDataset(ds)
-    add.GetArg("resampling").Set("average")
-    add.GetArg("min-size").Set(10)
+    add["dataset"] = ds
+    add["resampling"] = "average"
+    add["min-size"] = 10
     assert add.Run()
 
     assert ds.GetRasterBand(1).GetOverviewCount() == 1
 
     delete = get_overview_delete_alg()
-    delete.GetArg("dataset").Get().SetDataset(ds)
+    delete["dataset"] = ds
     assert delete.Run()
 
     assert ds.GetRasterBand(1).GetOverviewCount() == 0
diff --git a/autotest/utilities/test_gdalalg_raster_pipeline.py b/autotest/utilities/test_gdalalg_raster_pipeline.py
index 55ede9b0fa23..570ac85b8fd5 100755
--- a/autotest/utilities/test_gdalalg_raster_pipeline.py
+++ b/autotest/utilities/test_gdalalg_raster_pipeline.py
@@ -19,9 +19,7 @@
 
 
 def get_pipeline_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    raster = reg.InstantiateAlg("raster")
-    return raster.InstantiateSubAlgorithm("pipeline")
+    return gdal.GetGlobalAlgorithmRegistry()["raster"]["pipeline"]
 
 
 def test_gdalalg_raster_pipeline_read_and_write(tmp_vsimem):
@@ -68,11 +66,9 @@ def test_gdalalg_raster_pipeline_as_api(tmp_vsimem):
     out_filename = str(tmp_vsimem / "out.tif")
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("pipeline").Set(
-        f"read ../gcore/data/byte.tif ! write {out_filename}"
-    )
+    pipeline["pipeline"] = f"read ../gcore/data/byte.tif ! write {out_filename}"
     assert pipeline.Run()
-    ds = pipeline.GetArg("output").Get().GetDataset()
+    ds = pipeline["output"].GetDataset()
     assert ds.GetRasterBand(1).Checksum() == 4672
     assert pipeline.Finalize()
     ds = None
@@ -86,8 +82,8 @@ def test_gdalalg_raster_pipeline_input_through_api(tmp_vsimem):
     out_filename = str(tmp_vsimem / "out.tif")
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("input").Get().SetDataset(gdal.OpenEx("../gcore/data/byte.tif"))
-    pipeline.GetArg("pipeline").Set(f"read ! write {out_filename}")
+    pipeline["input"] = "../gcore/data/byte.tif"
+    pipeline["pipeline"] = f"read ! write {out_filename}"
     assert pipeline.Run()
     assert pipeline.Finalize()
 
@@ -100,8 +96,8 @@ def test_gdalalg_raster_pipeline_input_through_api_run_twice(tmp_vsimem):
     out_filename = str(tmp_vsimem / "out.tif")
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("input").Get().SetDataset(gdal.OpenEx("../gcore/data/byte.tif"))
-    pipeline.GetArg("pipeline").Set(f"read ! write {out_filename}")
+    pipeline["input"] = "../gcore/data/byte.tif"
+    pipeline["pipeline"] = f"read ! write {out_filename}"
     assert pipeline.Run()
     with pytest.raises(
         Exception, match=r"pipeline: Step nr 0 \(read\) has already an output dataset"
@@ -114,8 +110,8 @@ def test_gdalalg_raster_pipeline_output_through_api(tmp_vsimem):
     out_filename = str(tmp_vsimem / "out.tif")
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("output").Get().SetName(out_filename)
-    pipeline.GetArg("pipeline").Set("read ../gcore/data/byte.tif ! write")
+    pipeline["output"] = out_filename
+    pipeline["pipeline"] = "read ../gcore/data/byte.tif ! write"
     assert pipeline.Run()
     assert pipeline.Finalize()
 
@@ -126,7 +122,7 @@ def test_gdalalg_raster_pipeline_output_through_api(tmp_vsimem):
 def test_gdalalg_raster_pipeline_as_api_error():
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("pipeline").Set("read")
+    pipeline["pipeline"] = "read"
     with pytest.raises(Exception, match="pipeline: At least 2 steps must be provided"):
         pipeline.Run()
 
diff --git a/autotest/utilities/test_gdalalg_vector_clip.py b/autotest/utilities/test_gdalalg_vector_clip.py
index 9c5afbe0379a..0ec6a9fea798 100755
--- a/autotest/utilities/test_gdalalg_vector_clip.py
+++ b/autotest/utilities/test_gdalalg_vector_clip.py
@@ -20,9 +20,7 @@
 
 
 def get_clip_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    vector = reg.InstantiateAlg("vector")
-    return vector.InstantiateSubAlgorithm("clip")
+    return gdal.GetGlobalAlgorithmRegistry()["vector"]["clip"]
 
 
 @pytest.mark.require_driver("GPKG")
@@ -136,14 +134,14 @@ def test_gdalalg_vector_clip_bbox():
     src_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
+    clip["input"] = src_ds
 
     assert clip.ParseCommandLineArguments(
         ["--bbox", "0.2,0.3,0.7,0.8", "--of", "Memory", "--output", "memory_ds"]
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -169,7 +167,7 @@ def test_gdalalg_vector_clip_bbox_srs():
     src_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
+    clip["input"] = src_ds
 
     assert clip.ParseCommandLineArguments(
         [
@@ -185,7 +183,7 @@ def test_gdalalg_vector_clip_bbox_srs():
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     assert out_lyr.GetSpatialRef().GetAuthorityCode(None) == "4326"
     out_f = out_lyr.GetNextFeature()
@@ -220,14 +218,14 @@ def test_gdalalg_vector_clip_split_multipart():
     src_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
+    clip["input"] = src_ds
 
     assert clip.ParseCommandLineArguments(
         ["--bbox", "-0.1,0.3,1.1,0.7", "--of", "Memory", "--output", "memory_ds"]
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
 
     ref1_geom = ogr.CreateGeometryFromWkt(
@@ -284,14 +282,14 @@ def test_gdalalg_vector_clip_geom(clip_geom):
     src_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
+    clip["input"] = src_ds
 
     assert clip.ParseCommandLineArguments(
         ["--geometry", clip_geom, "--of", "Memory", "--output", "memory_ds"]
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -324,7 +322,7 @@ def test_gdalalg_vector_clip_geom_srs(clip_geom):
     src_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
+    clip["input"] = src_ds
     clip_geom = clip_geom.replace("0.2", "22263.8981586547")
     clip_geom = clip_geom.replace("0.3", "33395.9998333802")
     clip_geom = clip_geom.replace("0.7", "77923.6435552915")
@@ -343,7 +341,7 @@ def test_gdalalg_vector_clip_geom_srs(clip_geom):
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -376,7 +374,7 @@ def test_gdalalg_vector_clip_geom_not_rectangle():
     src_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
+    clip["input"] = src_ds
 
     assert clip.ParseCommandLineArguments(
         [
@@ -390,7 +388,7 @@ def test_gdalalg_vector_clip_geom_not_rectangle():
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -411,7 +409,7 @@ def test_gdalalg_vector_clip_intersection_incompatible_geometry_type():
     src_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
+    clip["input"] = src_ds
 
     assert clip.ParseCommandLineArguments(
         [
@@ -425,7 +423,7 @@ def test_gdalalg_vector_clip_intersection_incompatible_geometry_type():
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     assert out_lyr.GetNextFeature() is None
 
@@ -444,7 +442,7 @@ def test_gdalalg_vector_clip_intersection_promote_simple_type_to_multi():
     src_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
+    clip["input"] = src_ds
 
     assert clip.ParseCommandLineArguments(
         [
@@ -458,7 +456,7 @@ def test_gdalalg_vector_clip_intersection_promote_simple_type_to_multi():
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     ogrtest.check_feature_geometry(
@@ -487,13 +485,13 @@ def test_gdalalg_vector_clip_like_vector():
     like_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(["--of", "Memory", "--output", "memory_ds"])
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -525,8 +523,8 @@ def test_gdalalg_vector_clip_like_vector_invalid_geom():
     like_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(["--of", "Memory", "--output", "memory_ds"])
     with gdal.quiet_errors(), pytest.raises(
@@ -556,15 +554,15 @@ def test_gdalalg_vector_clip_like_vector_like_layer():
     like_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(
         ["--like-layer", "my_layer", "--of", "Memory", "--output", "memory_ds"]
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -585,8 +583,8 @@ def test_gdalalg_vector_clip_like_vector_like_layer_invalid():
     like_ds.CreateLayer("test")
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(
         ["--like-layer", "invalid", "--of", "Memory", "--output", "memory_ds"]
@@ -618,8 +616,8 @@ def test_gdalalg_vector_clip_like_vector_like_sql():
     like_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(
         [
@@ -633,7 +631,7 @@ def test_gdalalg_vector_clip_like_vector_like_sql():
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -672,15 +670,15 @@ def test_gdalalg_vector_clip_like_vector_like_where():
     like_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(
         ["--like-where", "id=1", "--of", "Memory", "--output", "memory_ds"]
     )
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -708,8 +706,8 @@ def test_gdalalg_vector_clip_like_vector_like_where_empty():
     like_lyr.CreateField(ogr.FieldDefn("id", ogr.OFTInteger))
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(
         ["--like-where", "id=1", "--of", "Memory", "--output", "memory_ds"]
@@ -745,13 +743,13 @@ def test_gdalalg_vector_clip_like_vector_srs():
     like_lyr.CreateFeature(f)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(["--of", "Memory", "--output", "memory_ds"])
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     ogrtest.check_feature_geometry(
@@ -777,13 +775,13 @@ def test_gdalalg_vector_clip_like_raster():
     like_ds.SetGeoTransform([0.2, 0.5, 0, 0.3, 0, 0.5])
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(["--of", "Memory", "--output", "memory_ds"])
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -818,13 +816,13 @@ def test_gdalalg_vector_clip_like_raster_srs():
     like_ds.SetSpatialRef(srs_3857)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(["--of", "Memory", "--output", "memory_ds"])
     assert clip.Run()
 
-    out_ds = clip.GetArg("output").Get().GetDataset()
+    out_ds = clip["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
     assert out_f["foo"] == "bar"
@@ -852,7 +850,7 @@ def test_gdalalg_vector_clip_geometry_invalid():
     src_ds.CreateLayer("test")
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
+    clip["input"] = src_ds
 
     assert clip.ParseCommandLineArguments(
         ["--geometry", "invalid", "--of", "Memory", "--output", "memory_ds"]
@@ -873,8 +871,8 @@ def test_gdalalg_vector_clip_like_vector_too_many_layers():
     like_ds = gdal.GetDriverByName("MEM").Create("", 1, 1, 1)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(["--of", "Memory", "--output", "memory_ds"])
     with pytest.raises(
@@ -895,8 +893,8 @@ def test_gdalalg_vector_clip_like_raster_no_geotransform():
     like_ds.CreateLayer("test2")
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(["--of", "Memory", "--output", "memory_ds"])
     with pytest.raises(
@@ -913,8 +911,8 @@ def test_gdalalg_vector_clip_like_neither_raster_no_vector():
     like_ds = gdal.GetDriverByName("Memory").Create("clip", 0, 0, 0, gdal.GDT_Unknown)
 
     clip = get_clip_alg()
-    clip.GetArg("input").Get().SetDataset(src_ds)
-    clip.GetArg("like").Get().SetDataset(like_ds)
+    clip["input"] = src_ds
+    clip["like"] = like_ds
 
     assert clip.ParseCommandLineArguments(["--of", "Memory", "--output", "memory_ds"])
     with pytest.raises(
diff --git a/autotest/utilities/test_gdalalg_vector_convert.py b/autotest/utilities/test_gdalalg_vector_convert.py
index b38ffc7a1241..b42be87d39b7 100755
--- a/autotest/utilities/test_gdalalg_vector_convert.py
+++ b/autotest/utilities/test_gdalalg_vector_convert.py
@@ -17,9 +17,7 @@
 
 
 def get_convert_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    vector = reg.InstantiateAlg("vector")
-    return vector.InstantiateSubAlgorithm("convert")
+    return gdal.GetGlobalAlgorithmRegistry()["vector"]["convert"]
 
 
 @pytest.mark.require_driver("GPKG")
@@ -156,8 +154,11 @@ def test_gdalalg_vector_wrong_layer_name(tmp_vsimem):
 
 def test_gdalalg_vector_convert_error_output_not_set():
     convert = get_convert_alg()
-    convert.GetArg("input").Get().SetName("../ogr/data/poly.shp")
-    convert.GetArg("output").Set(convert.GetArg("output").Get())
+    convert["input"] = "../ogr/data/poly.shp"
+
+    # Make it such that the "output" argment is set, but to a unset GDALArgDatasetValue
+    convert["output"] = convert["output"]
+
     with pytest.raises(
         Exception,
         match="convert: Argument 'output' has no dataset object or dataset name",
diff --git a/autotest/utilities/test_gdalalg_vector_filter.py b/autotest/utilities/test_gdalalg_vector_filter.py
index f0a62a97c65c..33b11a4239a3 100755
--- a/autotest/utilities/test_gdalalg_vector_filter.py
+++ b/autotest/utilities/test_gdalalg_vector_filter.py
@@ -15,9 +15,7 @@
 
 
 def get_filter_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    vector = reg.InstantiateAlg("vector")
-    return vector.InstantiateSubAlgorithm("filter")
+    return gdal.GetGlobalAlgorithmRegistry()["vector"]["filter"]
 
 
 def test_gdalalg_vector_filter_no_filter(tmp_vsimem):
@@ -27,7 +25,7 @@ def test_gdalalg_vector_filter_no_filter(tmp_vsimem):
     filter_alg = get_filter_alg()
     assert filter_alg.ParseCommandLineArguments(["../ogr/data/poly.shp", out_filename])
     assert filter_alg.Run()
-    ds = filter_alg.GetArg("output").Get().GetDataset()
+    ds = filter_alg["output"].GetDataset()
     assert ds.GetLayer(0).GetFeatureCount() == 10
     assert filter_alg.Finalize()
     ds = None
diff --git a/autotest/utilities/test_gdalalg_vector_info.py b/autotest/utilities/test_gdalalg_vector_info.py
index 9fbaace7eee7..524dcf104a14 100755
--- a/autotest/utilities/test_gdalalg_vector_info.py
+++ b/autotest/utilities/test_gdalalg_vector_info.py
@@ -19,9 +19,7 @@
 
 
 def get_info_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    vector = reg.InstantiateAlg("vector")
-    return vector.InstantiateSubAlgorithm("info")
+    return gdal.GetGlobalAlgorithmRegistry()["vector"]["info"]
 
 
 def test_gdalalg_vector_info_stdout():
@@ -42,14 +40,14 @@ def test_gdalalg_vector_info_stdout():
 def test_gdalalg_vector_info_text():
     info = get_info_alg()
     assert info.ParseRunAndFinalize(["--format=text", "data/path.shp"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     assert output_string.startswith("INFO: Open of")
 
 
 def test_gdalalg_vector_info_json():
     info = get_info_alg()
     assert info.ParseRunAndFinalize(["data/path.shp"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert j["layers"][0]["name"] == "path"
     assert "features" not in j["layers"][0]
@@ -58,7 +56,7 @@ def test_gdalalg_vector_info_json():
 def test_gdalalg_vector_info_features():
     info = get_info_alg()
     assert info.ParseRunAndFinalize(["--features", "data/path.shp"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert "features" in j["layers"][0]
 
@@ -68,7 +66,7 @@ def test_gdalalg_vector_info_sql():
     assert info.ParseRunAndFinalize(
         ["--sql", "SELECT 1 AS foo FROM path", "data/path.shp"]
     )
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert len(j["layers"][0]["fields"]) == 1
     assert j["layers"][0]["fields"][0]["name"] == "foo"
@@ -77,7 +75,7 @@ def test_gdalalg_vector_info_sql():
 def test_gdalalg_vector_info_layer():
     info = get_info_alg()
     assert info.ParseRunAndFinalize(["-l", "path", "data/path.shp"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert j["layers"][0]["name"] == "path"
 
@@ -92,7 +90,7 @@ def test_gdalalg_vector_info_wrong_layer():
 def test_gdalalg_vector_info_where(cond, featureCount):
     info = get_info_alg()
     assert info.ParseRunAndFinalize(["--where", cond, "data/path.shp"])
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert j["layers"][0]["featureCount"] == featureCount
 
@@ -110,6 +108,6 @@ def test_gdalalg_vector_info_dialect():
             "data/path.shp",
         ]
     )
-    output_string = info.GetArg("output-string").Get()
+    output_string = info["output-string"]
     j = json.loads(output_string)
     assert j["layers"][0]["features"][0]["properties"]["version"].startswith("3.")
diff --git a/autotest/utilities/test_gdalalg_vector_pipeline.py b/autotest/utilities/test_gdalalg_vector_pipeline.py
index d16968344b56..db93707735f7 100755
--- a/autotest/utilities/test_gdalalg_vector_pipeline.py
+++ b/autotest/utilities/test_gdalalg_vector_pipeline.py
@@ -19,9 +19,7 @@
 
 
 def get_pipeline_alg():
-    reg = gdal.GetGlobalAlgorithmRegistry()
-    vector = reg.InstantiateAlg("vector")
-    return vector.InstantiateSubAlgorithm("pipeline")
+    return gdal.GetGlobalAlgorithmRegistry()["vector"]["pipeline"]
 
 
 def test_gdalalg_vector_pipeline_read_and_write(tmp_vsimem):
@@ -68,9 +66,9 @@ def test_gdalalg_vector_pipeline_as_api(tmp_vsimem):
     out_filename = str(tmp_vsimem / "out.shp")
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("pipeline").Set(f"read ../ogr/data/poly.shp ! write {out_filename}")
+    pipeline["pipeline"] = f"read ../ogr/data/poly.shp ! write {out_filename}"
     assert pipeline.Run()
-    ds = pipeline.GetArg("output").Get().GetDataset()
+    ds = pipeline["output"].GetDataset()
     assert ds.GetLayer(0).GetFeatureCount() == 10
     assert pipeline.Finalize()
     ds = None
@@ -84,8 +82,8 @@ def test_gdalalg_vector_pipeline_input_through_api(tmp_vsimem):
     out_filename = str(tmp_vsimem / "out.shp")
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("input").Get().SetDataset(gdal.OpenEx("../ogr/data/poly.shp"))
-    pipeline.GetArg("pipeline").Set(f"read ! write {out_filename}")
+    pipeline["input"] = gdal.OpenEx("../ogr/data/poly.shp")
+    pipeline["pipeline"] = f"read ! write {out_filename}"
     assert pipeline.Run()
     assert pipeline.Finalize()
 
@@ -98,8 +96,8 @@ def test_gdalalg_vector_pipeline_input_through_api_run_twice(tmp_vsimem):
     out_filename = str(tmp_vsimem / "out.shp")
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("input").Get().SetDataset(gdal.OpenEx("../ogr/data/poly.shp"))
-    pipeline.GetArg("pipeline").Set(f"read ! write {out_filename}")
+    pipeline["input"] = gdal.OpenEx("../ogr/data/poly.shp")
+    pipeline["pipeline"] = f"read ! write {out_filename}"
     assert pipeline.Run()
     with pytest.raises(
         Exception, match=r"pipeline: Step nr 0 \(read\) has already an output dataset"
@@ -112,8 +110,8 @@ def test_gdalalg_vector_pipeline_output_through_api(tmp_vsimem):
     out_filename = str(tmp_vsimem / "out.shp")
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("output").Get().SetName(out_filename)
-    pipeline.GetArg("pipeline").Set("read ../ogr/data/poly.shp ! write")
+    pipeline["output"] = out_filename
+    pipeline["pipeline"] = "read ../ogr/data/poly.shp ! write"
     assert pipeline.Run()
     assert pipeline.Finalize()
 
@@ -124,7 +122,7 @@ def test_gdalalg_vector_pipeline_output_through_api(tmp_vsimem):
 def test_gdalalg_vector_pipeline_as_api_error():
 
     pipeline = get_pipeline_alg()
-    pipeline.GetArg("pipeline").Set("read")
+    pipeline["pipeline"] = "read"
     with pytest.raises(Exception, match="pipeline: At least 2 steps must be provided"):
         pipeline.Run()
 
@@ -624,10 +622,10 @@ def test_gdalalg_vector_pipeline_reproject_missing_layer_crs(tmp_vsimem):
     pipeline = get_pipeline_alg()
     mem_ds = gdal.GetDriverByName("Memory").Create("", 0, 0, 0, gdal.GDT_Unknown)
     mem_ds.CreateLayer("layer")
-    pipeline.GetArg("input").Get().SetDataset(mem_ds)
-    pipeline.GetArg("pipeline").Set(
-        f"read ! reproject --dst-crs=EPSG:4326 ! write {out_filename}"
-    )
+    pipeline["input"] = mem_ds
+    pipeline[
+        "pipeline"
+    ] = f"read ! reproject --dst-crs=EPSG:4326 ! write {out_filename}"
     with pytest.raises(
         Exception, match="reproject: Layer 'layer' has no spatial reference system"
     ):
diff --git a/swig/include/python/gdal_python.i b/swig/include/python/gdal_python.i
index 3421377200fb..db9a0ac37dcb 100644
--- a/swig/include/python/gdal_python.i
+++ b/swig/include/python/gdal_python.i
@@ -5251,6 +5251,92 @@ class VSIFile(BytesIO):
         return VSIFTellL(self._fp)
 %}
 
+
+/* -------------------------------------------------------------------- */
+/* GDALAlgorithmRegistryHS                                              */
+/* -------------------------------------------------------------------- */
+
+%extend GDALAlgorithmRegistryHS {
+%pythoncode %{
+
+    def __getitem__(self, key):
+        """Instantiate an algorithm
+
+           Shortcut for self.InstantiateAlg(key)
+
+           Example
+           -------
+           >>> gdal.GetGlobalAlgorithmRegistry()["raster"]
+        """
+
+        return self.InstantiateAlg(key)
+%}
+}
+
+/* -------------------------------------------------------------------- */
+/* GDALAlgorithmHS                                                      */
+/* -------------------------------------------------------------------- */
+
+%extend GDALAlgorithmHS {
+%pythoncode %{
+
+    def __getitem__(self, key):
+        """Get the value of an argument.
+
+           Shortcut for self.GetActualAlgorithm().GetArg(key).Get()
+           or self.InstantiateSubAlgorithm(key) for a non-leaf algorithm
+
+           Parameters
+           -----------
+           key: str
+               Name of a known argument of the algorithm
+           value:
+               Value of the argument
+
+           Example
+           -------
+           >>> alg["output-string"]
+           >>> alg["output"].GetName()
+           >>> alg["output"].GetDataset()
+           >>> gdal.GetGlobalAlgorithmRegistry()["raster"]["info"]
+        """
+
+        if self.HasSubAlgorithms():
+            return self.InstantiateSubAlgorithm(key)
+        else:
+            return self.GetActualAlgorithm().GetArg(key).Get()
+
+    def __setitem__(self, key, value):
+        """Set the value of an argment.
+
+           Shortcut for self.GetArg(key).Set(value)
+
+           Parameters
+           -----------
+           key: str
+               Name of a known argument of the algorithm
+           value:
+               Value of the argument
+
+           Examples
+           --------
+           >>> alg["bbox"] = [2, 49, 3, 50]
+           >>> alg["where"] = "country = 'France'"
+           >>> alg["input"] = "byte.tif"
+           >>> alg["input"] = gdal.Open("byte.tif")
+           >>> alg["target-aligned-pixels"] = True
+
+           >>> # Multiple input datasets
+           >>> alg["input"] = ["one.tif", "two.tif"]
+           >>> alg["input"] = [one_ds, two_ds]
+        """
+
+        if not self.GetArg(key).Set(value):
+            raise Exception(f"Cannot set argument {key} to {value}")
+%}
+}
+
+
 /* -------------------------------------------------------------------- */
 /* GDALAlgorithmArgHS                                                   */
 /* -------------------------------------------------------------------- */
@@ -5290,9 +5376,11 @@ class VSIFile(BytesIO):
             return self.SetAsDouble(value)
         if type == GAAT_DATASET:
             if isinstance(value, str):
-                return self.GetAsDatasetValue().SetName(value)
+                self.GetAsDatasetValue().SetName(value)
+                return True
             elif isinstance(value, Dataset):
-                return self.GetAsDatasetValue().SetDataset(value)
+                self.GetAsDatasetValue().SetDataset(value)
+                return True
             else:
                 return self.SetAsDatasetValue(value)
         if type == GAAT_STRING_LIST: