# How to use "gdal" CLI algorithms from Python

## Principles

"gdal" CLI algorithms are available as `osgeo.gdal.Algorithm` instances.

A convenient way to access an algorithm and run it is to use the `osgeo.gdal.Run()` function.

Run(*alg, arguments={}, progress=None, **kwargs)

  Run a GDAL algorithm and return it.

  Added in version 3.11.

  Parameters:

    - alg (str, list[str], tuple[str], Algorithm) -- Path to the algorithm or algorithm instance itself. For example "raster info", or ["raster", "info"] or "raster", "info".

    - arguments (dict) -- Input arguments of the algorithm. For example {"format": "json", "input": "byte.tif"}

    - progress (callable) -- Progress function whose arguments are a progress ratio, a string and a user data

    - kwargs -- Instead of using the `arguments` parameter, it is possible to pass algorithm arguments directly as named parameters of gdal.Run(). If the named argument has dash characters in it, the corresponding parameter must replace them with an underscore character. For example `dst_crs` as a a parameter of gdal.Run(), instead of `dst-crs` which is the name to use on the command line.

  Return type:

    a `osgeo.gdal.Algorithm` instance

If you do not need to access output value(s) of the algorithm, you can call `Run` directly: `gdal.Run(["raster", "convert"], input="in.tif", output="out.tif")`

The name of algorithm arguments are the long names as documented in the documentation page of each algorithm. They can also be obtained with `osgeo.gdal.Algorithm.GetArgNames()`.

    >>> gdal.Algorithm("raster", "convert").GetArgNames()
    ['help', 'help-doc', 'version', 'json-usage', 'drivers', 'config', 'progress', 'output-format', 'open-option', 'input-format', 'input', 'output', 'creation-option', 'overwrite', 'append']

For a command such as gdal raster info that returns a JSON output, you can get the return value of `osgeo.gdal.Run()` and call the `osgeo.gdal.Algorithm.Output()` method.

    alg = gdal.Run("raster", "info", input="byte.tif")
    info_as_dict = alg.Output()

If the return value is a dataset, `osgeo.gdal.Run()` can be used within a context manager, in which case `osgeo.gdal.Algorithm.Finalize()` will be called at the exit of the context manager.

    with gdal.Run("raster reproject", input=src_ds, output_format="MEM",
                  dst_crs="EPSG:4326") as alg:
        values = alg.Output().ReadAsArray()

## `gdal.alg` module

Added in version 3.12.

The `gdal.alg` module is also available with submodules and functions reflecting the hierarchy of algorithms. Functions return an `osgeo.gdal.Algorithm` instance similarly to `osgeo.gdal.Run()`

The above example running "gdal raster convert" can also be rewritten as:

    >>> from osgeo import gdal
    >>> gdal.alg.raster.convert(input="in.tif", output="out.tif")

The documentation of the function lists argument names, types and semantics:

    >>> from osgeo import gdal
    >>> help(gdal.alg.raster.convert)

        Help on function convert:

        convert(input: Union[List[osgeo.gdal.Dataset], List[str], List[os.PathLike[str]]], output: Union[osgeo.gdal.Dataset, str, os.PathLike[str]], input_format: Union[List[str], str, NoneType] = None, open_option: Union[List[str], str, NoneType] = None, output_format: Optional[str] = None, creation_option: Union[List[str], str, NoneType] = None, overwrite: Optional[bool] = None, append: Optional[bool] = None)
            Convert a raster dataset.

            Consult https://gdal.org/programs/gdal_raster_convert.html for more details.

            Parameters
            ----------
            input: Union[List[gdal.Dataset], List[str], List[os.PathLike[str]]]
                Input raster datasets
            output: Union[gdal.Dataset, str, os.PathLike[str]]
                Output raster dataset
            input_format: Optional[Union[List[str], str]]=None
                Input formats
            open_option: Optional[Union[List[str], dict, str]]=None
                Open options
            output_format: Optional[str]=None
                Output format ("GDALG" allowed)
            creation_option: Optional[Union[List[str], dict, str]]=None
                Creation option
            overwrite: Optional[bool]=None
                Whether overwriting existing output is allowed
            append: Optional[bool]=None
                Append as a subdataset to existing output

            Output parameters
            -----------------
            output: gdal.ArgDatasetValue
                Output raster dataset

## Raster commands examples

### Example 1: Getting information on a raster dataset as JSON

    from osgeo import gdal

    gdal.UseExceptions()
    info_as_dict = gdal.alg.raster.info(input="byte.tif").Output()

### Example 2: Converting a georeferenced netCDF file to cloud-optimized GeoTIFF

    from osgeo import gdal

    gdal.UseExceptions()
    gdal.alg.raster.convert(input="in.tif", output="out.tif", output_format="COG", overwrite=True)

or

    from osgeo import gdal

    gdal.UseExceptions()
    gdal.Run("raster", "convert", input="in.tif", output="out.tif",
             output_format="COG", overwrite=True)

or

    from osgeo import gdal

    gdal.UseExceptions()
    gdal.Run(["raster", "convert"], {"input": "in.tif", "output": "out.tif", "output-format": "COG", "overwrite": True})

### Example 3: Reprojecting a GeoTIFF file to a Deflate-compressed tiled GeoTIFF file

    from osgeo import gdal

    gdal.UseExceptions()
    gdal.alg.raster.reproject(
              input="in.tif", output="out.tif",
              dst_crs="EPSG:4326",
              creation_options={ "TILED": "YES", "COMPRESS": "DEFLATE"})

### Example 4: Reprojecting a (possibly in-memory) dataset to a in-memory dataset

    from osgeo import gdal

    gdal.UseExceptions()
    with gdal.alg.raster.reproject(input=src_ds, output_format="MEM",
                  dst_crs="EPSG:4326") as alg:
        values = alg.Output().ReadAsArray()

## Vector commands examples

### Example 5: Getting information on a vector dataset as JSON

    from osgeo import gdal

    gdal.UseExceptions()
    info_as_dict = gdal.alg.vector.info(input="poly.gpkg").Output()

### Example 6: Converting a shapefile to a GeoPackage

    from osgeo import gdal

    gdal.UseExceptions()
    gdal.alg.vector.convert(input="in.shp", output="out.gpkg", overwrite=True)

## Pipeline examples

### Example 7: Perform raster reprojection and gets the result as a streamed dataset.

    from osgeo import gdal

    gdal.UseExceptions()
    with gdal.alg.pipeline(pipeline="read byte.tif ! reproject --dst-crs EPSG:4326 --resampling cubic") as alg:
        ds = alg.Output()
        # do something with the dataset