MongoDB tip: comparing field cross collection using python

The goal is to find anything that's in col2, but not in col1.

col1 contains the following

col2 contains the following

Note, the field to compare in both collection need not to be in order as seen in the images.

Again, I am trying to find what's missing in the first set from the second set. 

from pymongo import MongoClient
import bson


client=MongoClient(host="mongodb://10.155.228.75:21001")

db=client.testJoe

col1=db.col1.distinct("compID");

col2= db.col2.distinct("compID");


col1= [int(x) for x in col1]

x = set(col2) - set(col1)
print(int(list(x)[0]))

we see the output is 7, which is the missing number from col1