Demonstrating efficient use of heapq.merge when working with arcpy.da.SearchCursor structures

heapq_merge.py

'''
Demonstrating efficient use of heapq.merge when working with
arcpy.da.SearchCursor structures. The heapq.merge function will
merge multiple sorted inputs into a single sorted output which
can be useful when iterating over multiple arcpy.da.SearchCursor
iterators.
'''

from pprint import pprint
import heapq
import itertools
import arcpy
arcpy.env.overwriteOutput = True
arcpy.env.workspace = r'C:\GIS\Temp\ArcGISHomeFolder\sample.gdb'

STATES = ['California', 'Texas', 'Arizona']
FC = (r'C:\Program Files (x86)\ArcGIS\Desktop10.5\TemplateData'
      r'\TemplateData.gdb\USA\cities')

# preparing the sample data by exporting individual feature classes
states_written = []
for state_name in STATES:
    state_name_normalized = state_name.replace(' ', '_')
    arcpy.Select_analysis(
        in_features=FC,
        out_feature_class='cities_{}'.format(state_name),
        where_clause='''STATE_NAME = '{}' '''.format(state_name_normalized),
    )
    states_written.append(state_name_normalized)

# getting the list of cursors for each individual feature class
cursors = [
    arcpy.da.SearchCursor(
        'cities_{}'.format(state_name),
        ['CITY_NAME', 'POP1990', 'STATE_NAME'],
        sql_clause=(None, 'ORDER BY POP1990 DESC'),
    ) for state_name in states_written
]

@profile
# ----------------------------------------------------------------------
def heapq_solution():
    # sort by the POP1990 field DESC
    merged = heapq.merge(*cursors, key=lambda x: x[1], reverse=True)
    # print 10 most populated cities in specified states
    result = list(itertools.islice(merged, 10))
    return result

@profile
# ----------------------------------------------------------------------
def sorted_solution():
    result = sorted(
        itertools.chain(*cursors), key=lambda x: x[1], reverse=True)
    return result

pprint(heapq_solution())

# resetting all da.SearchCursor to iterate over again
for cur in cursors:
    cur.reset()

pprint(sorted_solution()[:10])