Chapter 4 ineffective code, HELP!

[pydojo]

I download from https://github.com/GeospatialPython/Learn/blob/master/polygon.zip
unzipped polygon.zip get polygon.shp file and run codes below:

from osgeo import ogr
shape = ogr.Open("polygon.shp")
layer = shape.GetLayer()
feature = layer.GetNextFeature()
geom = feature.GetGeometryRef()
wkt = geom.ExportToWkt()
wkt

I get an error:

      1 shape = ogr.Open("polygon.shp")
----> 2 layer = shape.GetLayer()
      3 feature = layer.GetNextFeature()
      4 geom = feature.GetGeometryRef()
      5 wkt = geom.ExportToWkt()

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

Why? Is the data source missing something?

[pydojo]

After cp polygon.* to my cwd, everything is 👌