topic Re: Python statement in ArcGIS Pro Questions

Python statement

Eggnoggy — Thu, 19 Aug 2021 19:49:34 GMT

I am learning Python right now for ArcGIS Pro. I'm new to object-oriented programming and need some help on understanding the statement order. I'm basically looking for a simple logic breakdown for order of statements. For example:

aprx = arcpy.mp.ArcGISProject("CURRENT")

If I'm reading this correctly, a direct translation is:

variable = object.function(parameters)

So, the current project is a parameter of the function ArcGISProject being called on the object arcpy.mp, which will be stored in the variable aprx?

What about this:

m = aprx.activeMap

activeMap is a method called on the now object aprx and stored in the variable m?

lyrList = m.listLayers()

the listLayer function is being called on the now object m and stored in the variable lyrList?

And this:

for lyr in lyrList:
if lyr.isFeatureLayer:

a for-loop. It reads if a layers in the lyrList is a feature layer it gets stored as Boolean (T/F) in lyr?

Re: Python statement

DanPatterson — Thu, 19 Aug 2021 20:27:00 GMT

Looks good

Light reading .... see the table of contents to the left on this link

ArcGIS Pro Python reference—ArcGIS Pro | Documentation

Re: Python statement

DavidPike — Thu, 19 Aug 2021 21:19:40 GMT

I think that's a great understanding of how it works,

except I will say that activeMap is actually a property of aprx (the ArcGISProject object), not a method().

You then have associated the Map object returned from that property to 'm' using m = aprx.activeMap

see below link for the properties and methods of the ArcGISProject object/Class

https://pro.arcgis.com/en/pro-app/latest/arcpy/mapping/arcgisproject-class.htm

Re: Python statement

JoeBorgione — Thu, 19 Aug 2021 21:23:34 GMT

for lyr in lyrList:
if lyr.isFeatureLayer:

a for-loop. It reads if a layers in the lyrList is a feature layer it gets stored as Boolean (T/F) in lyr?

Not really. You need to do something when an if statement evaluates to True or False....

aprx = arcpy.mp.ArcGISProject("CURRENT") m = aprx.activeMap lyrList = m.listLayers() len(lyrList) # returns 11 for i in lyrList: print(i) Address Points Site Addresses Subdivisions_MSD MSD.SLCOMSD.AddressGridMSD RoadCenterline All CenterlinesMSD MunicipalitiesMSD MSD.SLCOMSD.ParcelsMSD MSD.SLCOMSD.Zones ZipcodesMSD World Imagery for i in lyrList: if i.isFeatureLayer: print('yay') ''' returns yay yay yay yay yay yay yay yay yay yay '''

Notice that while the length of my layer list = 11, when the if statement evaluates true, 'yay' is only printed 10 times. That's because the entry 'World Imagery' is not a feature layer. Use an else to capture that:

for i in lyrList: if i.isFeatureLayer: print('yay') else: print(f'{i} is not a feature layer') ''' returns yay yay yay yay yay yay yay yay yay yay World Imagery is not a feature layer '''

Re: Python statement

DanPatterson — Fri, 20 Aug 2021 02:16:18 GMT

And there goes the encouragement before the OP has even had a chance to read the links 😉