topic Re: Row.shape and .extent in Python Questions

Row.shape and .extent

JT2 — Sat, 11 Dec 2021 23:14:57 GMT

I was figuring out how to get a dataset's extent via python. In the help entry for extent I was intrigued to note the following sample code snippet:

for row in sCur:
    geom = row.shape
    ext = geom.extent

I am unable to find any information in the help files on the .shape class. Can anyone tell me about it? I had thought that you had to do something like this:

arcpy.Describe("Layer").extent.xmin

...so I was surprised to see this .shape.extent property. As far as I can see it's undocumented. Where am I going wrong, or where should I look? Thanks

Re: Row.shape and .extent

MathewCoyle — Tue, 05 Mar 2013 14:19:15 GMT

It is part of the geometry object and is definitely documented.

http://resources.arcgis.com/en/help/main/10.1/index.html#//018z00000070000000

Re: Row.shape and .extent

ChrisSnyder — Sat, 11 Dec 2021 23:15:00 GMT

To get the extent xmin bound of the entire layer:

arcpy.Describe("Layer").extent.XMin

To get the extent xmin bound of each feature in the layer:

searchRows = arcpy.da.SearchCursor("layer",["OID@","SHAPE@"])
for searchRow in searchRows:
    oidValue = searchRow[0]
    xminExt = searchRow[1].extent.XMin
    print "OID = " + str(oidValue) + " has an xmin extent of " + str(xminExt)

Re: Row.shape and .extent

JT2 — Sat, 11 Dec 2021 23:15:02 GMT

It is part of the geometry object and is definitely documented.

http://resources.arcgis.com/en/help/main/10.1/index.html#//018z00000070000000

Thanks for the pointer, but I cannot find any reference to .shape on the page you linked. There is no property of the Geometry class called 'shape'. So, as far as I can see, my original question stands: where is .shape documented?

Why does the following work, when the Row class doesn't even have a property called 'shape'? And why is there no object model diagram? It's so difficult to see how classes interact when you have to hop from one help entry to the other. We need a diagram to see how they fit together!

>>> cur = arcpy.SearchCursor("Landscan_Sample")
>>> for row in cur:
...     print row.shape.extent.XMax
... 
-10.8041666667

-10.7958333333

-10.7875

Re: Row.shape and .extent

MathewCoyle — Sat, 11 Dec 2021 23:15:05 GMT

Thanks for the pointer, but I cannot find any reference to .shape on the page you linked. There is no property of the Geometry class called 'shape'. So, as far as I can see, my original question stands: where is .shape documented?

Why does the following work, when the Row class doesn't even have a property called 'shape'? And why is there no object model diagram? It's so difficult to see how classes interact when you have to hop from one help entry to the other. We need a diagram to see how they fit together!
>>> cur = arcpy.SearchCursor("Landscan_Sample")
>>> for row in cur:
...     print row.shape.extent.XMax
... 
-10.8041666667

-10.7958333333

-10.7875

It accesses the shape field, which is a geometry object. You could get the same with

geom = row.getValue('Shape')

Re: Row.shape and .extent

JT2 — Thu, 07 Mar 2013 07:21:21 GMT

Oh I see, thanks for pointing that out. Yes, according to this page http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002z0000001q000000:

There are two basic ways to get and set field values on a row:
Using the field name, as in value = row.road_type
Using getValue and setValue, as in value = row.getValue("road_type")

How incredibly confusing that there's no way to tell if the .property is referring to a field name or a class/property. And what would happen if your field was called 'length'? Which takes precedence, the field name 'length', or the .length property of the Geometry class? How on earth are we meant to differentiate when reading others' code? Very confusing...

Re: Row.shape and .extent

MathewCoyle — Thu, 07 Mar 2013 12:11:08 GMT

The properties are all listed in the help which you linked to in a previous post. It is pretty simple to tell the difference. A property of row requires a parameter.

row.getValue(field)

Whereas a field referenced by the row object does not.

row.field

If for some reason you happen to have a row with the same name as a property, such as getValue, the property will take precedence. Your example of length doesn't work since it is a property of the geometry object not the row. It is accessed like this.

row.shape.length