# Create dictionary with segmentid as key, calculated length as value1, measured length as value2
fiberCableLengths = defaultdict(list)
with arcpy.da.SearchCursor(fiberCable, ['segmentid', 'calculatedlength', 'measuredlength']) as cursor:
    for row in cursor:
        fiberCableLengths[row[0]].append(row[1])
        fiberCableLengths[row[0]].append(row[2])
        
# Create slackloop dictionary with segmentidfkey as key, total up the length values of each slackloop under that segmentidfkey, and store as the dictionary value
slackloopLengths = defaultdict(list)
with arcpy.da.SearchCursor(slackLoop, ['segmentidfkey', 'length']) as cursor:
    for row in cursor:
        if row[1] is not None:
            slackloopLengths[row[0]].append(row[1])

# For each fibercable segmentid in dictionary, If calculated length + total slackloop length = measured length – Add to good list, Else – Add to bad list
goodList = []
badList = []
with arcpy.da.SearchCursor(fiberCable, ['segmentid', 'calculatedlength', 'measuredlength']) as cursor:
    for row in cursor:
        if row[1] + slackloopLengths[1] == row[2]:
            goodList.append[row[1]]
        else
            badList.append[row[1]]

The code above creates a dictionary where each item looks like the following: '1f169eae-5d7c-4ebb-90cd-abbe0e1b72dd': [50.0, 50.0, 50.0, 50.0]

How do I get it to sum the values for each key? The output I'd be looking for here would be: 4ebb-90cd-abbe0e1b72dd': [200]

Resources I've looked at:

https://stackoverflow.com/questions/4880960/how-to-sum-all-the-values-in-a-dictionary/4881100 https://stackoverflow.com/questions/34849651/how-to-add-the-values-of-dictionary-with-same-keys-in-python https://stackoverflow.com/questions/34849651/how-to-add-the-values-of-dictionary-with-same-keys-in-python