MapScript: Altering classes

Stephen Lime steve.lime at
Fri Jul 28 11:21:36 EDT 2000

Yes, for example:

  $class->setExpression('/^[A-Z]/') and for logical expressions $class->setExpression('([LENGTH] gt 50 and [AREA] < 150000)')


Stephen Lime
Internet Applications Analyst

Minnesota DNR
500 Lafayette Road
St. Paul, MN 55155

>>> "Michael Anderson" <m_anderson14 at> 07/28/00 10:21AM >>>
That did it. I didn't need to use the special characters either. Once again, 
thanks alot for the quick, correct answer. Does it work the same for regular 


>From: "Stephen Lime" <steve.lime at>
>To: <m_anderson14 at>
>CC: <mapserver-users at>
>Subject: Re: MapScript: Altering classes
>Date: Fri, 28 Jul 2000 09:53:36 -0500
>Problem (i think) is the expression setting. You need to use a special 
>method (nuts, forgot
>to update the website on this). Because several types of expressions are 
>supported it wasn't
>possible to use the standard way of setting values so a helper function was 
>The syntax is cl0.setExpression('N'). Basically the value for setExpression 
>*must* conform to
>the rules for expressions set in the map file docs. That may mean in 
>certain cirumstances
>that you may need to include a second set of quotes with strings with 
>spaces or special chars
>or just numbers (i.e. $class->setExpression("\"100\"")). I'll update the 
>website ASAP.
>Stephen Lime
>Internet Applications Analyst
>Minnesota DNR
>500 Lafayette Road
>St. Paul, MN 55155
> >>> "Michael Anderson" <m_anderson14 at> 07/28/00 09:45AM >>>
>I am trying to change the classification of a layer using MapScript. I
>change the colors in an existing classes with no problems, but if I try to
>set a new classitem and create new classes I get a segmentation error. Here
>is my code.
>map = mapObj("")
>soilsL = map.getLayerByName('soils')
>soilsL.classitem = 'Hydric_c'
>cl0 = classObj(soilsL)
>cl1 = classObj(soilsL)
>green = map.addColor(0,255,0)
>blue = map.addColor(0,0,255)
>black = map.addColor(0,0,0)
>cl0.expression = 'N'
>cl1.expression = 'Y'
>cl0.color = green
>cl1.color = blue
>cl0.outlinecolor = black
>cl1.outlinecolor = black
>soilsL.status = 1
>img = map.prepareImage()
>Segmentation fault -- kicked out of Python.
>I checked along the way to make sure my variables are referencing valid
>objects and everything looks OK. Can someone tell what I am doing wrong. I
>am guessing it has something to do with the expression, but it's only a
>guess. I can post a Perl version, but I think Python's syntax is clear
>enough to express what I am trying to do.
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