Get next element of cursor arcpy

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05-23-2017 03:59 PM
KyleDunaway1
New Contributor II

I am trying to compare two values, and can't seem to access the next row in a cursor.

for i, row in enumerate(cursor):

   if row[0] == cursor.next()[0]

Any ideas?

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RandyBurton
MVP Regular Contributor
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RandyBurton
MVP Regular Contributor
JoshuaBixby
MVP Esteemed Contributor

Beyond reading through the thread recommended by Randy Burton‌, a couple of questions:

  1. What type of cursor(s) are you working with?
  2. What happens if the condition is satisfied?

UPDATE:  continued....

As mentioned in the referenced GeoNet discussion, ArcPy cursors do not implement any kind of look- or read-ahead feature.  If one is working solely within DBMSs, there are likely set-based approaches that are better then using cursors for look-ahead functionality, .e.,g LAG and LEAD functionality implemented in many DBMSs; but one needs to work with what is available to them.

There are multiple ways to emulate look- or read-ahead functionality with Python and ArcPy, several are covered in the aforementioned GeoNet discussion.  Since I commented on that discussion last year, I have refined the approach I put forward.  Functionally, the approach below is not any different, but syntactically it is much more streamlined, I would argue more Pythonic.

from itertools import izip_longest

fc =   # path to feature class
flds = # string list of field names for cursors

with arcpy.da.SearchCursor(fc, flds) as n1_cur:
    with arcpy.da.UpdateCursor(fc, flds) as n_cur:
        filler_row = next(n1_cur)
        for n_row, n1_row in izip_longest(n_cur, n1_cur, fillvalue=filler_row):
            if n_row[0] == n1_row[0]:
                n_cur.updateRow([...])‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The basic approach is to pair a search cursor with an update cursor.  The search cursor is used for the look ahead (n+1 cursor or n1_cur) while the update cursor is used for the current record (n cursor or n_cur).  The itertools.izip_longest() function is used to pair the two cursors so they can be stepped through together, with the search cursor being one record ahead of the update cursor.

UPDATE 2:  Removed empty_row and created filler_row since previous code for empty_row would fail with datetime or geometry fields.