topic Re: How to get the value of a field from the first row without looping? in Python Questions

How to get the value of a field from the first row without looping?

SaidAkif — Thu, 26 Feb 2015 18:45:40 GMT

Hi all,

I am wondering how to get the value a field frorm the first row without looping through all the rows?

Thanks

Re: How to get the value of a field from the first row without looping?

RichardFairhurst — Fri, 10 Dec 2021 22:57:27 GMT

You still have to start a loop, but you can break out of it and kill the cursor at any time:

import arcpy
 
fc = 'c:/data/base.gdb/features'

# Open a cursor on some fields in a table
with arcpy.da.SearchCursor(fc, ['OID@', 'SHAPE@AREA']) as cursor:
     for row in cursor:
          # Do  something with the first row of data here

          break
del cursor

Re: How to get the value of a field from the first row without looping?

SaidAkif — Thu, 26 Feb 2015 19:01:12 GMT

I try and that works

Thanks all of you

Re: How to get the value of a field from the first row without looping?

JoshuaBixby — Fri, 10 Dec 2021 22:57:30 GMT

Since the arcpy.da.SearchCursor is an iterable that returns one list per row of the table/cursor, the Python built-in next() function can be used to retrieve the next row, which would be the first row if the cursor was just created or reset.

import arcpy  

fc = 'c:/data/base.gdb/features'  

# Open a cursor on some fields in a table  
with arcpy.da.SearchCursor(fc, ['OID@', 'SHAPE@AREA']) as cursor:
    row = next(cursor)
    # Do  something with the first row of data here

del cursor

Re: How to get the value of a field from the first row without looping?

NeilAyres — Fri, 10 Dec 2021 22:57:32 GMT

Or, something very similar, use the SearchCursor next method.

Cur = arcpy.da.SearchCursor(Feature, [Flds])
row = Cur.next()

Re: How to get the value of a field from the first row without looping?

XanderBakker — Fri, 27 Feb 2015 14:03:33 GMT

Or to use a one-liner:

value = arcpy.da.SearchCursor(in_fc, ("YourFieldName",)).next()[0]

Re: How to get the value of a field from the first row without looping?

SaidAkif — Fri, 27 Feb 2015 14:08:38 GMT

I try your code Xander and it work perfectly. That is really the easiest way to do it

Thanks for you all guys

Re: How to get the value of a field from the first row without looping?

JoshuaBixby — Fri, 27 Feb 2015 15:52:01 GMT

True, for now and in the ArcPy realm, calling the search cursor's next method will get the same result. I suggested using the built-in next method because of broader changes happening with Python outside of ArcPy. For Python 3 after PEP 3114 was approved, it meant the next() iterator method was going away. The Transition Plan for PEP 3114 covers two additional changes needed for moving to Python 3:

Method definitions named next will be renamed to __next__ .
Explicit calls to the next method will be replaced with calls to the built-in next function. For example, x.next() will become next(x) .

The built-in next function was introduced in Python 2.6 to smooth the transition. Since we know that Esri has made the leap to Python 3 with ArcGIS Pro, I suggested an approach using the built-in function. For now, Esri's implementation of the ArcPy Data Access (arcpy.da) module in ArcGIS Pro still includes cursors having explicit next() methods, but I argue the current ArcGIS Pro implementation isn't very pythonic since the explicit next() methods don't add any special functionality beyond simply iterating.

Re: How to get the value of a field from the first row without looping?

JoshuaBixby — Fri, 27 Feb 2015 15:55:48 GMT

If the cursor isn't going to be used once and disposed of, using a Python with statement ensures the cursor is reset for its next use. But then again, maybe having the cursor automatically reset isn't what someone wants. Just depends on the situation and need.

Re: How to get the value of a field from the first row without looping?

RustyRex — Wed, 05 Apr 2017 18:40:57 GMT

So to circle back, for the laymen, which approach would be the best to use?

Re: How to get the value of a field from the first row without looping?

JoshuaBixby — Fri, 10 Dec 2021 22:57:35 GMT

Several functionally equivalent code snippets were provided. I doubt the performance differences between the different code snippets will be noticeable, let alone significant. I think it is mostly a matter of style and what you prefer.

Lately, if I don't need to re-use the cursor, I have been using a variation of the one liner offered by Xander Bakker‌:

import arcpy

fc = 'c:/data/base.gdb/features'
values = next(arcpy.da.SearchCursor(fc, ['OID@', 'SHAPE@AREA']))‍‍‍‍