Setting reference frame for shapefile with pyshp?

Question

I'm using pyshp to create new shapefiles with Python 3. My code runs without errors, but when I open the resulting file in ArcMap I get this error:

The following datasource you added is missing spatial reference information.

This is not surprising, since I never told my code that the coordinates in the shapefile are supposed to be in EPSG:3006. How do I set this property in pyshp?

Here's some short example code. I want to tell the writer shape that the coordinates in start and stop are in EPSG:3006.

import shapefile

start = [6400137, 321751]  # Coordinates in EPSG:3006
stop  = [6400095, 319357]  # Coordinates in EPSG:3006

with shapefile.Writer("my_shapefile") as shape:
    shape.fileType = 3 # Polyline
    shape.field("FOO", "C", size = 32)
    shape.field("BAR", "C", size = 32)
    shape.line([[start, stop]])
    shape.record("foo", "bar")

Answer 1

Information about the coordinate system is stored in a separate projection file, that should have the same name as the shapefile, but a .prj extention.

As gene points out in comments, the Pyshp library doesn't handle projection files. So you will have to write the file yourself. Here's an example of how to do that:

# create the PRJ file
prj = open("%s.prj" % filename, "w")
epsg = 'GEOGCS["WGS 84",'
epsg += 'DATUM["WGS_1984",'
epsg += 'SPHEROID["WGS 84",6378137,298.257223563]]'
epsg += ',PRIMEM["Greenwich",0],'
epsg += 'UNIT["degree",0.0174532925199433]]'
prj.write(epsg)
prj.close()

If you want to find the correct file content for your coordinate system, I recommend you simply create a shapefile with that coordinate system in e.g. ArcCatalog, and then just copy paste the content of the created projection file.