[gdal-dev] OGR drivers written in Python

[Even Rouault]

Hi,

I've experimented lately with an infrastructure to write drivers in Python :
https://github.com/rouault/gdal2/tree/pythondrivers

This is a further step to the GDAL 2.2 new capability of writing pixel
functions in Python in VRT files.

For now, only read-only vector capabilities are supported.

The Python drivers don't depend on the SWIG Python bindings, so that can potentially be used
like native drivers, in all GDAL valid use cases: integrated in native code (GDAL command line
utilities, QGIS, etc..), GDAL SWIG Python bindings, fiona, etc...

Example: given the dummy driver in
https://github.com/rouault/gdal2/blob/pythondrivers/gdal/pythondrivers/ogr_MYPLUGIN.py

$ GDAL_PYTHON_DRIVER_PATH=pythondrivers ogrinfo -al -ro MYPLUGIN:

INFO: Open of `MYPLUGIN:'
      using driver `MYPLUGIN' successful.
Metadata:
  foo=bar

Layer name: my layer
Geometry: Point
Feature Count: 5
Extent: (2.100000, 49.000000) - (3.000000, 50.000000)
Layer SRS WKT:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,
        AUTHORITY["EPSG","9122"]],
    AUTHORITY["EPSG","4326"]]
FID Column = my_fid
Geometry Column = geomField
boolField: Integer(Boolean) (0.0)
intField: Integer (0.0)
int64Field: Integer64 (0.0)
realField: Real (0.0)
strField: String (0.0)
strNullField: String (0.0)
strUnsetField: String (0.0)
binaryField: Binary (0.0)
datetimeField: DateTime (0.0)
OGRFeature(my layer):1
  boolField (Integer(Boolean)) = 1
  intField (Integer) = 2
  int64Field (Integer64) = 1234567890123
  realField (Real) = 1.23
  strField (String) = foo
  strNullField (String) = (null)
  binaryField (Binary) = 010002
  datetimeField (DateTime) = 2017/04/26 12:34:56.789+00
  POINT (2 49)

[...]

OGRFeature(my layer):5
  boolField (Integer(Boolean)) = 1
  intField (Integer) = 6
  int64Field (Integer64) = 1234567890123
  realField (Real) = 1.23
  strField (String) = foo
  strNullField (String) = (null)
  binaryField (Binary) = 010002
  datetimeField (DateTime) = 2017/04/26 12:34:56.789+00
  POINT (2 49)

The PYTHONSO env variable can be used to force a given Python shared library
to be used, e.g PYTHONSO=libpython3.5m.so . I've tested with Python 2.6, 2.7,
3.2 and 3.5

Currently there's some copy&paste from the VRT Python derived band code that I'd
like to factor (the logic to dynamically load the Python interpreter and load
needed symbols)

The mechanism could probably be extended to support write operations
and the raster side too. I'm not sure how far I'll go with that, but I'll probably
write a RFC at some point with what exists.

Feedback welcome.

Even

-- 
Spatialys - Geospatial professional services
http://www.spatialys.com
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