python 2.7 - How to polygonize raster to shapely polygons

I am seeking an open-source python solution to convert raster to polygon (no ArcPy).

I did know the GDAL function to convert raster to polygon, and here is the manual: http://pcjericks.github.io/py-gdalogr-cookbook/raster_layers.html#polygonize-a-raster-band

Nevertheless, I expect that the output can be shapely polygons or any object, temporarily in memory, not saved as a file. Is there any package or code to handle this issue?

If the raster has been processed in a numpy array, the approach is listed below.

Answer

Use rasterio of Sean Gillies. It can be easily combined with Fiona (read and write shapefiles) and shapely of the same author.

In the script rasterio_polygonize.py the beginning is

import rasterio
from rasterio.features import shapes
mask = None
with rasterio.drivers():
    with rasterio.open('a_raster') as src:

        image = src.read(1) # first band
        results = (
        {'properties': {'raster_val': v}, 'geometry': s}
        for i, (s, v) 
        in enumerate(
            shapes(image, mask=mask, transform=src.affine)))

The result is a generator of GeoJSON features

 geoms = list(results)
 # first feature

 print geoms[0]
 {'geometry': {'type': 'Polygon', 'coordinates': [[(202086.577, 90534.3504440678), (202086.577, 90498.96207), (202121.96537406777, 90498.96207), (202121.96537406777, 90534.3504440678), (202086.577, 90534.3504440678)]]}, 'properties': {'raster_val': 170.52000427246094}}

That you can transform into shapely geometries

from shapely.geometry import shape
print shape(geoms[0]['geometry'])
POLYGON ((202086.577 90534.35044406779, 202086.577 90498.96206999999, 202121.9653740678 90498.96206999999, 202121.9653740678 90534.35044406779, 202086.577 90534.35044406779))

Create geopandas Dataframe and enable easy to use functionalities of spatial join, plotting, save as geojson, ESRI shapefile etc.

geoms = list(results)

import geopandas as gp
gpd_polygonized_raster  = gp.GeoDataFrame.from_features(geoms)