Properly writing floats to feature properties of a new shapefile in Fiona

Question

The following piece of code returns a shp following the driver and crs of a model .shp.

import numpy as np #just to test I correctly handle data types
import fiona
from shapely.geometry import Polygon, mapping
with fiona.open('model.shp') as source:
    source_driver = source.driver
    source_crs = source.crs
    #source_schema = source.schema
    source_schema = {'geometry': 'Polygon',
                 'properties': {'field_name': 'float'}} #Beware: field names cannot be longer than 10 characters!
        #writing a new file    
            with fiona.open('output.shp',
                            'w',
                             driver=source_driver,
                             crs=source_crs,
                             schema=source_schema) as collection:
                rec = {}
                rec['geometry'] = mapping(Polygon([(0,0),(1,0),(1,1),(0,0)]))
                rec['properties'] = {'field_name': float(np.float(0.3))}
                collection.write(rec)

The written record can be checked in this way:

collection = fiona.open('output.shp')
rec = collection.next()
print rec

Which returns: {'geometry': {'type': 'Polygon', 'coordinates': [[(0.0, 0.0), (1.0, 1.0), (1.0, 0.0), (0.0, 0.0)]]}, 'type': 'Feature', 'id': '0', 'properties': OrderedDict([(u'field_name', 0.3)])}

I followed @genes' hints from this post and @sgillies' recommendations below.

Answer 1

Shapefile fields are constrained to 10 chars, and so your 'a_fieldname' gets truncated by OGR (used by Fiona) to 'a_fieldname'. There might be a Fiona bug here. Workaround in the meanwhile is to change 'a_fieldname' in your schema to 'number' or something shorter than 10.