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Populate fields using python

TerryGustafson

I'm new to python and trying to figure out if this is possible. I have a measured layer with segments in it. I want to add a begin segment and end segment field. The layer has the following fields. Corridor, Ref Marker, shape length, beg_seg and end_seg. I would like to populate the begin seg and end seg from the shape_length field and accumulate them. So the mile post zero beg_seg would start at zero and the end_seg field would be the length of the zero segment. Then mile post 1 beg_seg would be the value of the end_seg of mile post one. The end_seg for mile post one would be the value of mile post 0 length plus the length of mile post one. this would continue till the last mile post. I have attached a image of the table that I manually entered the values for. I was hoping to create a python script to perform this as I have a ton of corridors with a ton of records. One other piece of information is some of the corridors may be missing mile posts.

sample.png

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TerryGustafson

I spoke to soon.. I have attached another sample.. I have a table that has multiple routes as shown so would want to build an array of the routes? then populate the fields?

list.png

TerryGustafson

Steelers going to win tonight?

jskinner

Since you are running this through the python window in ArcMap, you will only need to copy lines 5 - 33. Here are the steps:

1. Add the feature class to ArcMap

2. Change the fc variable in line 5 from 'Sample' to the feature class name

3. Open the python window

4. Copy lines 5 -33 and paste into the window

5. Click 'Enter' a couple of times to execute the code

TerryGustafson

Jake,

So this is how basic my knowledge is.. When I copy and paste this script into the python window how do I execute it? I have only done a little python scripting and used it in the field calculator..

jskinner

Hi Terry,

Try the following:

import arcpy
from arcpy import env
env.workspace = r"C:\temp\python\test.gdb"

fc = "Sample"

rmList = []

with arcpy.da.SearchCursor(fc, ["RM"]) as cursor:
    for row in cursor:
        rmList.append(row[0])

del cursor

rmList.sort()

for RM in rmList:
    if RM == 0:
        with arcpy.da.UpdateCursor(fc, ["RM", "SHAPE_LEN", "beg_seg", "end_seg"], "RM = " + str(RM)) as cursor:
            for row in cursor:
                row[2] = 0
                length = row[1]
                row[3] = length                
                cursor.updateRow(row)
    else:
        with arcpy.da.UpdateCursor(fc, ["RM", "SHAPE_LEN", "beg_seg", "end_seg"], "RM = " + str(RM)) as cursor:
            for row in cursor:
                row[2] = length
                newLength = row[1]
                row[3] = length + newLength                
                cursor.updateRow(row)
                length = row[3]
del cursor

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