topic Re: Help w/ py code (just a correction) in Python Questions

Help w/ py code (just a correction)

RafaelRuas_Martins — Tue, 08 Nov 2016 17:42:40 GMT

I need some help to correct a bug on this simple py code.

I have been using it w/ no problem since I up graded ArcGIS Desktop from 10.3 to 10.4.

# The code below adds one point at a time to a selection and

# calculates area of convex hull of the selection.

# Output is a text file (or table) with with two columns.

# First column holds number of points selected,

# second column holds total area of the hull.

# Provided you want to use all points in the feature class.

# I recommend you use square metres to get the area and do

# the conversion yourself if you need to. If square metres

# result in too large numbers, use square kilmetres.

import arcpy

# PARAMETERS

in_points = arcpy.GetParameterAsText(0)

# column indicating in what order to add points to the curve

# should be integers from 1 to N by 1

sort_field = 'OBJECTID'

out_results = arcpy.GetParameterAsText(1)

out_delim = ","

# we need to store the hull temporarily;

# there are more ways how to deal with intermediate data, this is a simple one

arcpy.env.overwriteOutput = True

tmp_hull = arcpy.GetParameterAsText(2)

# WORK

# write header for result file

with open(out_results, "w") as fl:

header = out_delim.join(("PT_COUNT", "M_SQ"))

fl.write(header + "\n")

# total number of points

n = int(arcpy.GetCount_management(in_points).getOutput(0))

# we need a feature layer in order to make quick selections

in_points_lyr = arcpy.management.MakeFeatureLayer(in_points, "points").getOutput(0)

for i in range(n):

print i

# add another point to the selecition

w_clause = '"%s" < %s' % (sort_field, i + 1) # e.g. OBJECTID < 1, OBJECTID < 2, ...

arcpy.management.SelectLayerByAttribute(in_points_lyr, "NEW_SELECTION", w_clause)

# counstruct convex hull

hull = arcpy.management.MinimumBoundingGeometry(in_points_lyr, tmp_hull, "CONVEX_HULL", "ALL").getOutput(0)

# get the area of the convex hull

# (if you coordinate system units are metres)

ara = 0

with arcpy.da.SearchCursor(hull, ["SHAPE@AREA"]) as sc:

for row in sc:

ara += row[0] # should be just one row anyway

# write results for i into the result file

with open(out_results, "a") as fl:

result = out_delim.join((str(i + 1), str(ara)))

fl.write(result + "\n")

print("Script completed.")

That's the error message!!!

Re: Help w/ py code (just a correction)

DanPatterson_Retired — Tue, 08 Nov 2016 18:37:43 GMT

Rafael, you will have to format your code so it is readable

/blogs/dan_patterson/2016/08/14/script-formatting

Re: Help w/ py code (just a correction)

NeilAyres — Sat, 11 Dec 2021 08:58:34 GMT

As Dan says, without proper formatting, it is very hard to tell.

But what is your select clause supposed to be doing?

# add another point to the selecition


w_clause = '"%s" < %s' % (sort_field, i + 1) # e.g. OBJECTID < 1, OBJECTID < 2, ...


arcpy.management.SelectLayerByAttribute(in_points_lyr, "NEW_SELECTION", w_clause)
‍‍‍‍‍‍‍

The other thing is, have you considered just running this as a plain python script before you turn it into a script tool, with all the extra that entails.

Re: Help w/ py code (just a correction)

DarrenWiens2 — Sat, 11 Dec 2021 08:58:37 GMT

Try using AddFieldDelimiters to handle the quotes:

>>> fc = 'points'
... sort_field = 'FID'
... w_clause = arcpy.AddFieldDelimiters(fc, sort_field) + ' < ' + str(5) # or str(i+1)
... arcpy.SelectLayerByAttribute_management(fc,"NEW_SELECTION",w_clause)‍‍‍‍‍‍‍‍

Re: Help w/ py code (just a correction)

RafaelRuas_Martins — Tue, 08 Nov 2016 23:44:20 GMT

Hi everyone.

The problem is the variable SORT FIELD = "OBJECTID" and the data had no OBJECTID field. It had OID field.

It's quite simple. I am a rookie in Python.

Next time, I will post the sample code as Dan Patterson and Neil Ayres suggested.

Thanks all!!!!

Re: Help w/ py code (just a correction)

DanPatterson_Retired — Tue, 08 Nov 2016 23:49:35 GMT

Rafael...

Shapefiles will have a FID and generally an OID field, the first is required, the 2nd is sometimes generated.

Geodatabase featureclasses will have the OBJECTID field.

Re: Help w/ py code (just a correction)

DarrenWiens2 — Sat, 11 Dec 2021 08:58:40 GMT

Glad you figured it out. If you want to save yourself this headache in the future, you can get the unique ID field dynamically like this:

>>> fc = 'myFeatureLayer'
... print arcpy.Describe(fc).OIDFieldName
... 
FID‍‍‍‍