I was asked about a seemingly simple line of code in one of my scripts and I didn't have an immediate answer. After a few pages of g-search, I'm still a bit stumped, but not afraid to ask for the answer!
facFC = arcpy.CreateFeatureclass_management("in_memory", "facFC", "POINT")[0]
What exactly is the [0] at the end of this statement for?
There's examples of having it there and other examples it's not found.
Thanks!
I had a similarly "fuzzy" response when I got the question, I had a hunch that [0] is an index position but not exactly sure to what.
Note! there is no ….. blah = CreateFeatureclass
I am able to reference facFC var on the next line in order to add a field:
facFC = arcpy.CreateFeatureclass_management("in_memory", "facFC", "POINT")[0]
arcpy.AddField_management(facFC, "NAME", "TEXT", None, None, 40, "", "NULLABLE", "NON_REQUIRED")
Thank you for the response!
I never liked shortcuts that obscure …
It is 'ok' but not recommended since putting in the featureclass name as a parameter doesn't hide the fact and relying on slicing might lead you to slice the wrong parameter the next time for the next tool that you use.
I second what Dan Patterson mentioned. I normally define the output and other variable at the start of the script and use in this case the os module to split the path and name in a path and a name. Something like this:
import arcpy
import os
fc_out = r'C:\some\path\to\outputfgdb.gdb\YourFeatureclass'
ws, fc_name = os.path.split(fc_out)
arcpy.CreateFeatureclass_management(ws, fc_name, etc)
arcpy.AddField_management(fc_out, YourFieldName, etc)I believe the [0] indicates the first item in the Result object returned from the tool, which happens to be the new feature class name.
Using tools in Python—Geoprocessing and Python | ArcGIS Desktop
As Darren points out, nearly all geoprocessing tools return Result—Help | ArcGIS Desktop objects, which explains the ArcGIS/ArcPy side of your question.
For the Python side of your question, Python classes can emulate container objects by implementing certain special methods: 3. Data model - Emulating Container Types— Python 2.7.15 documentation. Support for the indexing and slicing operator, i.e., [], is implemented using the object.__getitem__ special method. For the ArcPy Result object, the __getitem__ special method either points to Result.getOutput() or implements the same code.
In short, Result[0] is the same as calling Result.getOutput(0) .
Create Feature Class—Data Management toolbox | ArcGIS Desktop
the [0] is a slice, meaning get the first, which in your case would be the first... first of what is sketchy.
The above is the preferred by me, approach,
out_path…. the location where the featureclass is going
out_name .. the name to give the featureclass
geometry_type… point, line, polygon stuff
template … if you have a featureclass that you want to use for emulation
has_m, has_z - well? do you want them?
spatial_reference - specify it now! or you have to use the define projection tool
the rest... might be important but not critical if saving to a gdb which would have the info anyway.
Note! there is no ….. blah = CreateFeatureclass
because everything is inside the function