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Language bindings: Python

2011 January 28

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Test environment


Linux Debian:
just to be sure to check an up-to-date state-of-the-art I've actually used Debian Squeeze (32 bit). So I'm actually sure that all required packages are reasonably using the most recent version.

Python:
python-2.6.6 was already installed on my testbed system, so I was immediately ready to start my test.

pyspatialite connector:
the connector source is available for download at: http://code.google.com/p/pyspatialite/
I've actually downloaded the latest supported version: http://pyspatialite.googlecode.com/files/pyspatialite-2.6.1.tar.gz
In order to build and install the pyspatialite connector I used the canonical Python scripts:

$ python setup.py build
... verbose output follows [suppressed] ...
$ su
# python setup.py install

Very important notice: I soon discovered that simply using the standard build script wasn't enough: this way I got an obsolete SpatiaLite v.2.3.1 and that's not at all a good thing.

Caveat

The most recent QGIS versions (1.6 / 1.7 trunk) are actually using SpatiaLite v.2.4.0 so any Python plugin using the previous v.2.3.1 can easily cause conflicts due to version incompatilibiles.
And this fully accounts for any issue noticed by QGIS users.

Patching setup.py


I quickly discovered that supporting the most recent SpatiaLite v.2.4.0-RC4 was actually a piece of cake: I simply had to change two lines in the setup.py script (line 87 and followings).

def get_amalgamation():
    """Download the Spatialite amalgamation if it isn't there, already."""
    if os.path.exists(AMALGAMATION_ROOT):
        return
    os.mkdir(AMALGAMATION_ROOT)
    print "Downloading amalgation."

    # find out what's current amalgamation ZIP file
    download_page = urllib.urlopen("http://www.gaia-gis.it/spatialite-2.4.0-4/sources.html").read()
    pattern = re.compile("(libspatialite-amalgamation.*?\.zip)")
    download_file = pattern.findall(download_page)[0]
    amalgamation_url = "http://www.gaia-gis.it/spatialite-2.4.0-4/"+ download_file
    zip_dir = string.replace(download_file,'.zip','')
    # and download it
    urllib.urlretrieve(amalgamation_url, "tmp.zip")

Once I applied such a trivial patch anything ran in the smoothest and most pleasant way.


Python sample program

spatialite_sample.py
# importing pyspatialite
from pyspatialite import dbapi2 as db

# creating/connecting the test_db
conn = db.connect('test_db.sqlite')

# creating a Cursor
cur = conn.cursor()

# testing library versions
rs = cur.execute('SELECT sqlite_version(), spatialite_version()')
for row in rs:
    msg = "> SQLite v%s Spatialite v%s" % (row[0], row[1])
    print msg

# initializing Spatial MetaData
# using v.2.4.0 this will automatically create
# GEOMETRY_COLUMNS and SPATIAL_REF_SYS
sql = 'SELECT InitSpatialMetadata()'
cur.execute(sql)

# creating a POINT table
sql = 'CREATE TABLE test_pt ('
sql += 'id INTEGER NOT NULL PRIMARY KEY,'
sql += 'name TEXT NOT NULL)'
cur.execute(sql)
# creating a POINT Geometry column
sql = "SELECT AddGeometryColumn('test_pt',
" sql += "'geom', 4326, 'POINT', 'XY')"
cur.execute(sql)

# creating a LINESTRING table
sql = 'CREATE TABLE test_ln ('
sql += 'id INTEGER NOT NULL PRIMARY KEY,'
sql += 'name TEXT NOT NULL)'
cur.execute(sql)
# creating a LINESTRING Geometry column
sql = "SELECT AddGeometryColumn('test_ln', "
sql += "'geom', 4326, 'LINESTRING', 'XY')"
cur.execute(sql)

# creating a POLYGON table
sql = 'CREATE TABLE test_pg ('
sql += 'id INTEGER NOT NULL PRIMARY KEY,'
sql += 'name TEXT NOT NULL)'
cur.execute(sql)
# creating a POLYGON Geometry column
sql = "SELECT AddGeometryColumn('test_pg', "
sql += "'geom', 4326, 'POLYGON', 'XY')"
cur.execute(sql)

# inserting some POINTs
# please note well: SQLite is ACID and Transactional
# so (to get best performance) the whole insert cycle
# will be handled as a single TRANSACTION
for i in range(100000):
    name = "test POINT #%d" % (i+1)
    geom = "GeomFromText('POINT("
    geom += "%f " % (i / 1000.0)
    geom += "%f" % (i / 1000.0)
    geom += ")', 4326)"
    sql = "INSERT INTO test_pt (id, name, geom) "
    sql += "VALUES (%d, '%s', %s)" % (i+1, name, geom)
    cur.execute(sql)
conn.commit()

# checking POINTs
sql = "SELECT DISTINCT Count(*), ST_GeometryType(geom), "
sql += "ST_Srid(geom) FROM test_pt"
rs = cur.execute(sql)
for row in rs:
    msg = "> Inserted %d entities of type " % (row[0])
    msg += "%s SRID=%d" % (row[1], row[2])
    print msg

# inserting some LINESTRINGs
for i in range(100000):
    name = "test LINESTRING #%d" % (i+1)
    geom = "GeomFromText('LINESTRING("
    if (i%2) == 1:
    # odd row: five points
        geom += "-180.0 -90.0, "
        geom += "%f " % (-10.0 - (i / 1000.0))
        geom += "%f, " % (-10.0 - (i / 1000.0))
        geom += "%f " % (10.0 + (i / 1000.0))
        geom += "%f" % (10.0 + (i / 1000.0))
        geom += ", 180.0 90.0"
    else:
    # even row: two points
        geom += "%f " % (-10.0 - (i / 1000.0))
        geom += "%f, " % (-10.0 - (i / 1000.0))
        geom += "%f " % (10.0 + (i / 1000.0))
        geom += "%f" % (10.0 + (i / 1000.0))
    geom += ")', 4326)"
    sql = "INSERT INTO test_ln (id, name, geom) "
    sql += "VALUES (%d, '%s', %s)" % (i+1, name, geom)
    cur.execute(sql)
conn.commit()

# checking LINESTRINGs
sql = "SELECT DISTINCT Count(*), ST_GeometryType(geom), "
sql += "ST_Srid(geom) FROM test_ln"
rs = cur.execute(sql)
for row in rs:
    msg = "> Inserted %d entities of type " % (row[0])
    msg += "%s SRID=%d" % (row[1], row[2])
    print msg

# inserting some POLYGONs
for i in range(100000):
    name = "test POLYGON #%d" % (i+1)
    geom = "GeomFromText('POLYGON(("
    geom += "%f " % (-10.0 - (i / 1000.0))
    geom += "%f, " % (-10.0 - (i / 1000.0))
    geom += "%f " % (10.0 + (i / 1000.0))
    geom += "%f, " % (-10.0 - (i / 1000.0))
    geom += "%f " % (10.0 + (i / 1000.0))
    geom += "%f, " % (10.0 + (i / 1000.0))
    geom += "%f " % (-10.0 - (i / 1000.0))
    geom += "%f, " % (10.0 + (i / 1000.0))
    geom += "%f " % (-10.0 - (i / 1000.0))
    geom += "%f" % (-10.0 - (i / 1000.0))
    geom += "))', 4326)"
    sql = "INSERT INTO test_pg (id, name, geom) "
    sql += "VALUES (%d, '%s', %s)" % (i+1, name, geom)
    cur.execute(sql)
conn.commit()

# checking POLYGONs
sql = "SELECT DISTINCT Count(*), ST_GeometryType(geom), "
sql += "ST_Srid(geom) FROM test_pg"
rs = cur.execute(sql)
for row in rs:
    msg = "> Inserted %d entities of type " % (row[0])
    msg += "%s SRID=%d" % (row[1], row[2])
    print msg

rs.close()
conn.close()
quit()

$ python spatialite_sample.py

Telling the full story is boring and very few interesting: you can study and test the sample code by yourself, and that's absolutely all.

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CC-BY-SA logo Author: Alessandro Furieri a.furieri@lqt.it
This work is licensed under the Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) license.

GNU logo Permission is granted to copy, distribute and/or modify this document under the terms of the
GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.