polygon - How to read a shapefile in Python?

My question is an extension of Vertical lines in a polygon shapefile. Kindly refer to that question first.

What you will see is a method of generating vertical lines with respect to the bounding box, at user-defined spacing. I understand that OGR, Fiona, Shapely etc. can be used to do the next step of clipping, but I do not understand their utilization.

How do I read one line of a polygon shapefile? Every application that uses Shapely shows how to generate the LineString, Point or Polygon but never to read an existing shapefile

Kindly assist me with at-least a skeleton structure so I can build on it.

Answer

1) read your shapefile with Fiona, PyShp, ogr or ...using the geo_interface protocol (GeoJSON):

with Fiona

import fiona
shape = fiona.open("my_shapefile.shp")
print shape.schema
{'geometry': 'LineString', 'properties': OrderedDict([(u'FID', 'float:11')])}
#first feature of the shapefile
first = shape.next()
print first # (GeoJSON format)

{'geometry': {'type': 'LineString', 'coordinates': [(0.0, 0.0), (25.0, 10.0), (50.0, 50.0)]}, 'type': 'Feature', 'id': '0', 'properties': OrderedDict([(u'FID', 0.0)])}

with PyShp

import shapefile
shape = shapefile.Reader("my_shapefile.shp")
#first feature of the shapefile
feature = shape.shapeRecords()[0]
first = feature.shape.__geo_interface__  
print first # (GeoJSON format)
{'type': 'LineString', 'coordinates': ((0.0, 0.0), (25.0, 10.0), (50.0, 50.0))}

with ogr:

from osgeo import ogr
file = ogr.Open("my_shapefile.shp")
shape = file.GetLayer(0)
#first feature of the shapefile
feature = shape.GetFeature(0)
first = feature.ExportToJson()
print first # (GeoJSON format)
{"geometry": {"type": "LineString", "coordinates": [[0.0, 0.0], [25.0, 10.0], [50.0, 50.0]]}, "type": "Feature", "properties": {"FID": 0.0}, "id": 0}

2) conversion to Shapely geometry (with the shape function)

# now use the shape function of Shapely
from shapely.geometry import shape
shp_geom = shape(first['geometry']) # or shp_geom = shape(first) with PyShp)
print shp_geom
LINESTRING (0 0, 25 10, 50 50)
print type(shp_geom)

3) computations

4) save the resulting shapefile