Coding issue - trying to update single FC using SearchCursor & UpdateCursor

Question

Fairly new to python and I have a issue with writing new values to an existing text field in a feature class/shapefile. I want to update the existing text values by taking the Shape@ geometry of the polygon and making a series of text values seperated by a comma. I got it to work to create the text line and I can write the lines to a file - but now I want to take that text string and replace the values in a field that are already there using UpdateCursor. I want to make sure that all the polygon vertices are written to one filed, then move onto the next polygon as well - here I am trying to compare the OID's - if they change then move on. I am having issues accomplishing that feat - I can get the values to display in the python window - but then I get a "Runtime error Traceback (most recent call last): File "", line 21, in TypeError: value #1 - unsupported type: list"

Here is my code so far:

import arcpy
infc = "H:\GIST_8125\Oil_Gas\Gail_test\clip_project.shp"
for row in arcpy.da.SearchCursor(infc, ["OID@", "SHAPE@", "Coord_stri"]):
 # iterate through polygon parts
 partnum = 0
 for part in row [1]:
 # list polygon part points
 for pnt in part:
 print (str(pnt.X) + ',' + str(pnt.Y))
 partnum += 1
# update coord_string
with arcpy.da.UpdateCursor(infc, ["OID@", "Coord_stri"]) as uCursor:
#iterate through rows and update values
 for row in uCursor:
 if row [0] == row [0]:
 row [1] = ([pnt.X, pnt.Y])
 uCursor.updateRow(row)
del uCursor, row

---

The first part of the polygon is correctly being written to the field - now just need to find a way to write the 4 other points to the same line:

import arcpy
infc = "H:\GIST_8125\Oil_Gas\Gail_test\clip_project.shp"
uCursor = arcpy.da.UpdateCursor(infc, ["OID@", "SHAPE@", "Coord_stri"])
for row in uCursor:
 # iterate through polygon parts
 partnum = 0
 for part in row [1]:
 # list polygon part points
 for pnt in part:
 print (str(pnt.X) + ',' + str(pnt.Y))
 row[2] = (str(pnt.X) + ',' + str(pnt.Y))
 uCursor.updateRow(row)
 partnum += 1
del uCursor, row

• SMiller: Your "Coord_stri" field is a text field and can't support a list. Instead of using the list [pnt.X, pnt.Y], convert the list to a string. e.g. coordlist = [pnt.X, pnt.Y] coordstr = ",".join(coordlist) row[1] = coordstr.
• SMiller: Actually I wonder if a Field Calculator might be a better option in this case. I think the Field Calculator (available in interactive mode or via arcpy) can access the SHAPE@ field and break it down.

Answer 1

Add the shape token (SHAPE@) to the UpdateCursor and you dont need the SearchCursor:

import arcpy
fc = r"H:\GIST_8125\Oil_Gas\Gail_test\clip_project.shp"
with arcpy.da.UpdateCursor(fc,['SHAPE@','Coord_stri']) as cursor:
 for row in cursor:
 coords = []
 part = row[0].getPart(0)
 for pnt in part:
 coords.extend([pnt.X, pnt.Y])
 row[1]=', '.join(str(c) for c in coords)
 cursor.updateRow(row)

• Gail Robertson: BERA - thank you SO much for the editing - it works like a charm! All the parts of the polygon are correctly added to the "coord_stri: field as needed. I do have a question though - why only specify the (str(x) for x in coords) - and not mention the y?
• Bera: Nice! x is just a variable name, I should have called it something else less confusing. x is in this case each coordinate (both x and y's) in the list called coords. I have changed it to c. Could you accept my answer with the checkbox?
• Gail Robertson: Thank you for the clarity BERA - good stuff! Checked as requested - this stack exchange dedicated to Geo is a fantastic resource - could not have done it without you and smiller!

Answer 2

Your "Coord_stri" field is a text field and can't support a list. Instead of using the list [pnt.X, pnt.Y], convert the list to a string. e.g. coordlist = [pnt.X, pnt.Y] coordstr = ",".join(coordlist) row[1] = coordstr.

(You could also combine these statements as below):

with arcpy.da.UpdateCursor(infc, ["OID@", "Coord_stri"]) as uCursor:
#iterate through rows and update values
 for row in uCursor:
 if row [0] == row [0]:
 row [1] = ",".join(map(str, [pnt.X, pnt.Y])) #creates a list from the pnt values, joins the list by comma into a string, uses that string as value for "Coord_stri"
 uCursor.updateRow(row)

• Gail Robertson: Thanks smiller - I think it is so close... when I run in Arc - I get an error:Runtime error Traceback (most recent call last): File "<string>", line 20, in <module> TypeError: sequence item 0: expected string, float found - I think that is coming from the Shape@ geometry as numbers - do I need to covert from float to string in the update cursor... ?
• SMiller: Yes, I think you're on the right track -- or you could just do this all at once (either with map python function, or row[1] = ",".join([str(pnt.X), str(pnt.Y]))
• SMiller: I think this is the one-liner: row[1] = " ,".join(map(str,[pnt.X, pnt.Y]))