[Mapserver-users] Python MapScript: setting string attributes to None

[Sean Gillies]

Dear Mapserving Pythoneers,

For some time we've been enduring the inconvenience that
string attributes of map objects (such as layer.group),
once set, cannot be undefined.  This is due to a quirk in
the Python wrapper code that SWIG emits.

I've just committed into CVS a fix for this problem.  Part
of the fix is in mapscript.i so, unless you are comfortable
with using SWIG, you may have to wait a while until the
nightly system creates an updated Python wrapper code.  The
rest of the fix relies on a new setup script called
'setup_wnone.py'.

After rebuilding and installing the Python MapScript using
setup_wnone.py, you will be able to undefine string attributes
of your map objects with statements like:

    thelayer.[ATTRIBUTE] = None

This update to Python MapScript affects _only_ attributes
that are accessed directly (through __setattr__).  For attributes
like a class expression, continue to use

    theclass.setExpression('')

to undefine the expression.  For color attributes, continue to
use statements like

    null = colorObj()
    null.red, null.green, null.blue = (-1, -1, -1)
    theclass.styles.outlinecolor = null

peace,
Sean

--
Sean Gillies
sgillies at frii.com
http://www.frii.com/~sgillies