Python MapScript Appendix

Author:

Sean Gillies

Author:

Seth Girvin

Contact:

sethg at geographika.co.uk

Last Updated:

2021-05-24

Introduction

The Python MapScript module contains some class extension methods that have not yet been implemented for other languages.

Classes

References to sections below will be added here as the documentation grows.

imageObj

Pillow (a fork of the Python Imaging Library), https://pillow.readthedocs.io/, is an indispensable tool for image manipulation. The extensions to imageObj are all geared towards better integration of Pillow in MapScript applications.

imageObj Extended Methods

• imageObj.write() - write image data to a Python file-like object. Default is stdout.

url = urllib.urlopen('https://mapserver.org/_static/banner.png')
ms_image = imageObj(url, 'AGG/JPEG')

See MapScript Image Generation for further examples.

pointObj

pointObj Methods

__str__()string

Return a string formatted like

{ 'x': %f , 'y': %f, 'z': %f }

with the coordinate values substituted appropriately. Usage example:

>>> p = mapscript.pointObj(1, 1, 1)
>>> str(p)
{ 'x': 1 , 'y': 1, 'z': 1 }

Note that the return value can be conveniently eval’d into a Python dictionary:

>>> p_dict = eval(str(p))
>>> p_dict['x']
1

rectObj

rectObj Methods

__contains__( pointObj point )boolean

Returns True if point is inside the rectangle, otherwise returns False.

>>> r = mapscript.rectObj(0, 0, 1, 1)
>>> p = mapscript.pointObj(2, 0)       # outside
>>> p in r
False
>>> p not in r
True

__str__()string

Return a string formatted like

{ 'minx': %f , 'miny': %f , 'maxx': %f , 'maxy': %f }

with the bounding values substituted appropriately. Usage example:

>>> r = mapscript.rectObj(0, 0, 1, 1)
>>> str(r)
{ 'minx': 0 , 'miny': 0 , 'maxx': 1 , 'maxy': 1 }

Note that the return value can be conveniently eval’d into a Python dictionary:

>>> r_dict = eval(str(r))
>>> r_dict['minx']
0

Exception Handling

The Python MapScript module maps a few MapServer errors into Python exceptions. Attempting to load a non-existent Mapfile raises an ‘IOError’, for example

>>> import mapscript
>>> mapfile = '/no/such/file.map'
>>> m = mapscript.mapObj(mapfile)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/lib/python2.3/site-packages/mapscript.py", line 799, in __init__
    newobj = _mapscript.new_mapObj(*args)
IOError: msLoadMap(): Unable to access file. (/no/such/file.map)
>>>

The message of the error is written by ‘msSetError’ and so is the same message that CGI mapserv users see in error logs.