Writing ArcPy UpdateCursor based on row test?

Question

I'm working on building a series of updates to street feature class based on fields inside the class. I was attempting to do this with update cursor to get better performance.

When the Streets_GC_FullName is null, the STREETS_NW_SLIPRD = 2 and STREETS_NW_RAMP=1, then change the Streetname field to "Exit Ramp"

The Cursor runs for a little while but then none of the rows are actually updated. I had tried adding the print statment to see if it was stopping on those rows that matched, but none printed.

So I'm assuming that my row test is failing?

fc = r'C:\GIS\Sept2018_MergeLA.gdb\NW_GC'
fields = ['Streets_GC_FULLNAME', 'Streets_NW_FEATTYP', 'Streets_NW_SLIPRD', 'Streets_NW_RAMP', 'StreetName','Streets_NW_ID']

with arcpy.da.UpdateCursor(fc, fields) as cursor:
    for row in cursor:
        if (row[0] is None and row[3] == 2 and row[4] == 1):
            row[5] == "Exit Ramp"
            # print("Updated"+row[6])
            cursor.updateRow(row)
print ("Processing complete")

Answer 1

There are three problems with your code that I can see:

PROBLEM 1:

The line row[5] == "Exit Ramp" should use = (assign a value) not == (testing for equality). row[5] is not actually being assigned a value by the statement as it is. In fact nothing at all is being done by that statement.

PROBLEM 2:

Your row indexes appear to be a bit muddled. You have 6 fields in your cursor. They are zero-indexed so the last field is row[5], not row[6]. So I would expect that the (commented out) print statement would crash if uncommented (and processing actually reached that point).

Your fields are:

fields = ['Streets_GC_FULLNAME', 'Streets_NW_FEATTYP', 'Streets_NW_SLIPRD', 'Streets_NW_RAMP', 'StreetName','Streets_NW_ID']

So...

• row[0] is 'Streets_GC_FULLNAME'
• row[1] is 'Streets_NW_FEATTYP'
• row[2] is 'Streets_NW_SLIPRD'
• row[3] is 'Streets_NW_RAMP'
• row[4] is 'StreetName'
• row[5] is 'Streets_NW_ID'
• row[6] DOES NOT EXIST and is an out-of-range index

So your if statement translates to something like:

if (Streets_GC_FULLNAME is None and Streets_NW_RAMP == 2 and StreetName == 1)

Do you really have any features with StreetName == 1 ? I would guess that StreetName is a string, so testing for equality with 1 is probably not what you really want.

PROBLEM 3:

Assuming problem 1 gets fixed...

Similarly, row[5] = "Exit Ramp" (single '=') would translate to something like Streets_NW_ID = "Exit Ramp"

From your question, I don't think this is what you intended.

Solution:

You said in your question that you wanted to test for:

Streets_GC_FullName is null, the STREETS_NW_SLIPRD = 2 and STREETS_NW_RAMP=1, then change the Streetname field to "Exit Ramp"

This should be something like (untested):

        if row[0] is None and row[2] == 2 and row[3] == 1
            row[4] = "Exit Ramp"
            print "Updated {}".format(row[5])
            cursor.updateRow(row)