Select by attributes within the fiona Python module

Question

Is it possible to select polygons from a shapefile based upon their attributes using the Fiona Python module? I can't seem to find anything in the docs, but it seems like a strange thing not to be included in the module.

All I can think of at the moment is iterating through all the polygons, doing the calculations I want to do, and then storing the data in a database, or some other data structure, and then running my SELECT query over that.

Alternatively if there is another Python module that will do this easily then that would be great to know about.

Answer 1

Sure.

import fiona
with fiona.open("file.shp") as src:
 filtered = filter(lambda f: f['properties']['foo']=='bar', src)

It's documented at https://fiona.readthedocs.io/en/latest/manual.html#slicing-and-masking-iterators

The thing is: shapefiles don't have standard and interoperable attribute indexes and so you have to loop over all features and test them no matter what. If you want high performing indexes, load your shapefiles into a relational database and create all the indexes you need.

• user1186: thanks for the soln @sgillies, when I try to do sink.write(feature), it does not create anything in the attribute table of the new shapefile. Any idea why? I am happy to create a new question.

Answer 2

If you want to select by a list of attributes you can do something like this:

import fiona
inp_list = ['region1','region2','region3']
with fiona.open("OriginalShape.shp") as input:
 meta = input.meta
 with fiona.open('OutputShape.shp', 'w',**meta) as output:
 for feature in input:
 if feature['properties']['foo'] in inp_list:
 output.write(feature)

This will create a new shapefile with only the selected attributes.