Error getting while creating new field to a shapefile table

Question

I am getting the error for following code to add a new field to a shapefile table.

from osgeo import ogr
# Open a Shapefile, and get field names
source = ogr.Open('my.shp', 1)
layer = source.GetLayer()
layer_defn = layer.GetLayerDefn()
field_names = [layer_defn.GetFieldDefn(i).GetName() for i in range(layer_defn.GetFieldCount())]
print len(field_names), 'MYFLD' in field_names
# Add a new field
new_field = ogr.FieldDefn('MYFLD', ogr.OFTInteger)
layer.CreateField(new_field)
# Close the Shapefile
source = None

Error is as following:

layer = source.GetLayer()

AttributeError: 'NoneType' object has no attribute 'GetLayer'

Answer 1

This is because 'my.shp' did not open successfully or the file did not exist, thus source is None.

It's a good idea to test if the file exists, and to see if the file opened properly:

import os
from osgeo import ogr
fname = 'my.shp' # change this for your example
if not os.path.isfile(fname):
 raise FileNotFoundError('Could not find file ' + str(fname))
source = ogr.Open(fname, 1)
if source is None:
 raise ValueError('Could open file ' + str(fname))
...

---

Another strategy is to enable exceptions (which will be the default for GDAL 4.0):

ogr.UseExceptions()

This will raise RuntimeError exceptions, e.g. when files cannot be found or opened.

• vamsi: Hi Mike, thanks for giving such a good solution..But still i am getting error even i loaded my shape file into QGis application. Error getting as "could not find file"..please suggest me a solution..Thanks, Bhavya
• Mike T: Try specifying an absolute path to the file: unix path: fname = '/home/name/gis/my.shp'; or Windows: fname = r'C:\Users\name\Documents\GIS\my.shp'
• vamsi: Hi..Mike i came out of the above problem..Thanks u so much for your great support towards solving my problem..