topic Re: List comprehension with statement using arcpy.da cursors? in Python Questions

List comprehension with statement using arcpy.da cursors?

ChrisSnyder — Fri, 10 Aug 2012 17:29:18 GMT

Excited to get my hands dirty using the arcpy.da module, and I appreciate the reasoning for the optional "with" statement syntax.

Question:

While it is possible to do this:

tileList = [r[0] for r in arcpy.da.SearchCursor(freq1Tbl, "TILE_NO")]

it doesn't seem possible to do this:

tileList = [row[0] for row in cursor with arcpy.da.SearchCursor(freq1Tbl, "TILE_NO") as cursor]

Am I using the wrong syntax here, or can you just not use the with statement in a list/dictionary comprehension?

Re: List comprehension with statement using arcpy.da cursors?

JasonScheirer — Fri, 10 Aug 2012 19:44:27 GMT

The with statement does not work in a list comprehension, no. There's no need for it assuming the comprehension does not throw an exception, though. Once a da cursor runs out of rows it closes itself in the same manner as it would leaving a with block.

Re: List comprehension with statement using arcpy.da cursors?

ChrisSnyder — Mon, 13 Aug 2012 15:07:39 GMT

Thanks Jason... In the docs I saw the part about the with statement "guarantee close and release of database locks and reset iteration", and thought that sounded good, but as long as the cursor executes successfully I guess that does that anyway.