Summing Values for Each Item in a Dictionary

Question

# 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(int(row[1]))

sumValueDict = {k: sum(v) for k, v in slackloopLengths.items()}

# 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:
        for k, v in sumValueDict.items():
            if row[0] == k:
                if row[1] and row[2] is not None:
                    if int(row[1]) + int(v) == int(row[2]):
                        goodList.append(str(row[0]))
                        print "Good List: " + row[0]
                        print int(row[1]) + int(v)
                        print int(row[2])
                    else:
                        badList.append(str(row[0]))
                        print "Bad List: " + row[0]
                        print int(row[1]) + int(v)
                        print int(row[2])
print "Good List Size: " + str(len(goodList))
print "Bad List Size: " + str(len(badList))

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

Answer 1

Iterate over the dict items and construct a new dict from the key and sum of the values:

>>> slackloopLength = {'abc': [1,2,4,7], 'def': [1,3,5,7,9]}
>>> {k: sum(v) for k, v in slackloopLength.items()}
{'abc': 14, 'def': 25}
>>> 

The way to read this construction is:

We're going to make a dict:

   { 

and each element will have key k and value sum(v):

   {k: sum(v)

where k and v are each of the key-value pairs of elements of slackloopLength:

   {k: sum(v) for k, v in slackloopLength.items()}