Greedy Cow Transport

[perfringo]

is j value and i key:value pair in your code?

You can easily test what is what

In [1]: from itertools import combinations                                                         

In [2]: d = {'Maggie': 3, 'Herman': 7, 'Betsy': 9, 'Oreo': 6, 'Moo Moo': 3, 'Milkshake': 2,  
   ...:      'Millie': 5, 'Lola': 2, 'Florence': 2, 'Henrietta': 9}                                

In [3]: list(combinations(d, 2))[:5]   # first five combinations to see what we get                                                              
Out[3]: 
[('Maggie', 'Herman'),
 ('Maggie', 'Betsy'),
 ('Maggie', 'Oreo'),
 ('Maggie', 'Moo Moo'),
 ('Maggie', 'Milkshake')]

We get key pair combinations, but they don't have values. With this part we 'put values back and convert to dict': {j: d[j] for j in i} - from each pair we take individual keys and construct new dictionary by getting key and its corresponding value from original dictionary.

For first row in pair combinations ('Maggie', 'Herman'):

{j: d[j] for j in i} --> {'Maggie': d['Maggie'], 'Herman': d['Herman']} --> {'Maggie': 3, 'Herman': 7}

For sake of readabilty the d[j] could be replaced with d.get(j) - this gives better understanding that we will 'get' value of j.