How to compare dictionaries and see what changed?

Question

I am having 3 dictionaries in my python code :

1. self.new_port_dict = {} # Dictionary to store the new ports from curr_host
2. self.old_port_dict = {} # Dictionary to store the old ports from old_host
3. self.results_ports_dict = {} # Holds the result of changed/newly added ports

The script needs to compare what port changed, I am almost there just unable to present help me out :

      def comp_ports(self,filename):
          try:
                f = open(filename)
                self.prev_report = pickle.load(f) # NmapReport

                for s in self.prev_report.hosts:
                    self.old_port_dict[s.address] = set()
                    for x in s.get_open_ports():
                        self.old_port_dict[s.address].add(x)

                for s in self.report.hosts:
                    self.new_port_dict[s.address] = set()
                    for x in s.get_open_ports():
                       self.new_port_dict[s.address].add(x)

                print "The following Host/ports were available in old scan : !!"
                print `self.old_port_dict`
                print "--------------------------------------------------------"
                print "The following Host/ports have been added in new scan:  !!"
                print `self.new_port_dict`
                for h in self.old_port_dict.keys():
                 self.results_ports_dict[h] = self.new_port_dict[h]- self.old_port_dict[h]
                 print "Result Change: for",h ,"->",self.results_ports_dict[h]         

 except Exception as l:
             print l

This gives a output as :

The following Host/ports were available in old scan : !!
{'172.16.0.41': set([(80, 'tcp'), (666, 'tcp')]), '172.16.0.163': set([(80, 'tcp'), (22, 'tcp')])}
--------------------------------------------------------
The following Host/ports have been added in new scan:  !!
{'172.16.0.41': set([(80, 'tcp'), (22, 'tcp')]), '172.16.0.163': set([(80, 'tcp'), (22, 'tcp')])}

Result Change: for 172.16.0.41 -> set([(22, 'tcp')])  From set([(80, 'tcp'), (666, 'tcp')])

Result Change: for 172.16.0.163 -> set([])  From set([(80, 'tcp'), (22, 'tcp')])

As you can clearly see , I have the resulting changed dictionary as well. I want to just print :

    For "host_name" , Port changed from "port_id" to "new_port_id" 

ex: For 172.16.0.41, Port changed from (666, 'tcp')  to  (22, 'tcp')

Answer 1

Based on Alex Martelli's answer on Is there a better way to compare dictionary values

You can do this :

#eval the differences between the 2 dict:
diff_key=[key for key in old_port_dict if old_port_dict[key]!=new_port_dict[key]]
for key in diff_key:
    print "For %s, Port changed from %s to %s" %(key,old_port_dict[key],new_port_dict[key])