Iteratively Filling a Dictionary and Updating a Feature Class

Question

import arcpy

fiberCable = r'C:\Users\broadhurstn\Documents\ArcGIS\Default.gdb\FIBERCABLE'
fibercableToConduit = r'C:\Users\broadhurstn\Documents\ArcGIS\Default.gdb\FibercableToConduit'
conduit = r'C:\Users\broadhurstn\Documents\ArcGIS\Default.gdb\CONDUIT'

# Populate a dictionary that maps segment ID to the placed/planned date
segment_dates = {}
with arcpy.da.SearchCursor(fiberCable, ['segmentid', 'bv_cable_placed_planned']) as cursor:
    for row in cursor:
        segment_dates[row[0]] = row[1]

# Populate a dictionary that maps conduit ID to a two-item list containing segment ID and placed/planned date
ftcs = {}
with arcpy.da.SearchCursor(fibercableToConduit, ['conduitipid', 'segmentid']) as cursor:
    for row in cursor:
        # Use .get() so that it won't fail if a segment ID isn't in the dictionary
        ftcs[row[0]] = [row[1], segment_dates.get(row[1])]

# Populate conduit 'bv_placed_est' field        
with arcpy.da.UpdateCursor(conduit, ['ipid', 'bv_placed_est_1']) as cursor:
    for row in cursor:
        for k, v in ftcs.items():
            if row[0] == k:
                row[1] = str(v[1])
                cursor.updateRow(row)

The above code and feature class table produce a dictionary that fills as follows: {'daac02d0-bf62-4968-b1cd-0fe36c391b2f': ['55a16ddd-2d1d-443b-9935-ecafd2bc7d3b']

How do I add a second value to the dictionary using the below feature class table?

Notice how the value in the dictionary matches "segment ID" in this feature class. I want to have the the SearchCursor look at the current dictionary, see if there is a value that matches the "SegmentID" field values and append the field "Cable Placed Planned" to it's corresponding dictionary item as a second value.

Expected output for the first item:

{'daac02d0-bf62-4968-b1cd-0fe36c391b2f': ['55a16ddd-2d1d-443b-9935-ecafd2bc7d3b', '3/28/2020']

What I've created so far, which doesn't work correctly:

with arcpy.da.SearchCursor(FIBERCABLE, ['segmentid', 'bv_cable_placed_planned']) as cursor:
    for row in cursor:
        if FTCDICT[str(row[0])] == str(row[0]):
            FTCDICT[str(row[1])] = str(row[1])

Answer 1

The most efficient way is to create two dictionaries:

1. Map segment ID to placed/planned date
2. Map conduit ID to your desired list by using the first dictionary

Here's an example:

import arcpy

tbl_cables = 'FIBERCABLE'
tbl_ftc = 'FTC'

field_segment = 'segmentid'
field_conduit = 'conduitipid'
field_date = 'bv_cable_placed_planned'

# Populate a dictionary that maps segment ID to the placed/planned date
segment_dates = dict()
with arcpy.da.SearchCursor(tbl_cables, [field_segment, field_date]) as cursor:
    for row in cursor:
        segment_dates[row[0]] = row[1]

# Populate a dictionary that maps conduit ID to a two-item list containing segment ID 
# and placed/planned date
ftcs = dict()
with arcpy.da.SearchCursor(tbl_ftc, [field_conduit, field_segment]) as cursor:
    for row in cursor:
        # Use .get() so that it won't fail if a segment ID isn't in the dictionary
        ftcs[row[0]] = [row[1], segment_dates.get(row[1])]

Answer 2

You can use collections.defaultdict(list):

from collections import defaultdict
import arcpy

FTC = r'C:\data.gdb\features'
FIBERCABLE = r'C:\data.gdb\cables'

d = defaultdict(list)
with arcpy.da.SearchCursor(FTC, ['conduitipid', 'segmentid']) as cursor:
    for con, seg in cursor:
        d[con].append(seg)

d2 = {k:v for k,v in arcpy.da.SearchCursor(FIBERCABLE,['Segment ID','Cabled Placed Planned'])}

for key, val in d.iteritems(): #d.items() in py3
    if val[0] in d2:
        d[key].append(d2[val[0]])