Yours truly, Fiona

Fiona now writes feature collections to disk. Here's a bit of code from the tests, dressed up with extra comments:

from fiona import collection
from shapely import asShape, mapping

# Open a source of features
with collection("docs/data/test_uk.shp", "r") as source:

    # Define a schema for the feature sink
    schema = input.schema.copy()
    schema['geometry'] = 'Point'

    # Open a new sink for features
    with collection(
        "test_write.shp", "w", driver="ESRI Shapefile", schema=schema
        ) as sink:

        # Process only the features intersecting a box
        for f in source.filter(bbox=(-5.0, 55.0, 0.0, 60.0)):

            # Get their centroids using Shapely
            f['geometry'] = mapping(asShape(f['geometry']).centroid)

            # Stage feature for writing

    # The sink shapefile is written to disk when its ``with`` block ends

That's just 9 statements. Fiona isn't just about less code, it's about taking advantage of Python built-ins and idioms to shrink the API's cranial memory footprint. You already know dicts, and data are better than objects, so features are modeled as GeoJSON-like mappings. Feature schemas are mappings, too. You already know how Python file I/O works, so persisted featured collections are modeled like files. Obviousness and familiarity are what I'm going for here. If you have to call help(fiona) more than 8 times in your entire life, I'll have failed.

I still need to work on support for writing geometry types other than 'Point', coordinate reference systems and make sure it's tight memory-wise (Fiona is all C underneath). It also might be nice to let the sink collection's schema be set from the first written feature, making the above example only 7 statements. The OGR library is so loaded with features – making a simple wrapper API is almost entirely about saying no and throwing features out. And how I've thrown things out. Geometries, out. Fields, out. Features, out. Cursors, out. Layers, out. There's almost nothing left except "open file", "filter iterator", "next dict", "append dict" and "close file". It almost goes without saying that this is for minimalists only.

Update (2011-12-10): the "writing" branch of Fiona now writes polylines and polygons. Multipart geometry types coming soon.


Re: Yours truly, Fiona

Author: Nathan W

Very cool! Nice job. I like the look of this very much and how much more readable it makes OGR. I have tried a few times to use OGR from Python and while it wasn't hard it still felt very "this is a C++ API with Python on top" this makes it feel a lot more native Python.

Will keep an eye on the projects progress.

Re: Yours truly, Fiona

Author: Sean

Thanks, Nathan. Follow on GitHub if you haven't already and let me know how the library suits your own data access needs.