arcpy.da Cursors and Readability Part 2

arcpy.da cursors provide the simplest data structure by default (tuples). Python generators provide a pretty neat way of customizing these cursors to increase readability.


Return dict instead of tuple:

def rows_as_dicts(cursor):
  """ returns rows as dicts (does not maintain field order) """
  colnames = cursor.fields
  for row in cursor:
    yield dict(zip(colnames, row))

Usage (note the cursor is wrapped with the generator):

total_cost_by_name = {}
with arcpy.da.SearchCursor(costs_table, ["name", "unit_cost", "quantity"]) as curs:
  for row in rows_as_dicts(curs):
    total_cost_by_name[row["name"]] = row["unit_cost"] * row["quantity"]

If using with an update cursor, you’ll want to use an OrderedDict so the field/value order is maintained. You’ll also need to the use dict.values() to pass an ordered tuple back into Cursor.updateRow.


Return collections.OrderedDict instead of tuple:

import collections
def rows_as_ordered_dicts(cursor):
  """ returns rows as collections.OrderedDict """
  colnames = cursor.fields
  for row in cursor:
    yield collections.OrderedDict(zip(colnames, row))

Usage (updating):

with arcpy.da.UpdateCursor(costs_table, ["unit_cost", "quantity", "total_cost"]) as curs:
  for row in rows_as_ordered_dicts(curs):
    row["total_cost"] = row["unit_cost"] * row["quantity"]

    # call .values() to convert back to tuple
    # if we didn't use OrderedDict, the values would be in random order.
    curs.updateRow( row.values() )
comments powered by Disqus