CODEWITHSUNDEEP
pythondictionary
VeilEclipse
VeilEclipse

Reputation: 2856

Python Merge 2 Dictionaries without overwriting

If a and b are 2 dictionaries:

a = {'UK':'http://www.uk.com', 'COM':['http://www.uk.com','http://www.michaeljackson.com']}



bb = {'Australia': 'http://www.australia.com', 'COM':['http://www.Australia.com', 'http://www.rafaelnadal.com','http://www.rogerfederer.com']}

I want to merge them to get

{'Australia': ['http://www.australia.com'], 'COM': ['http://www.uk.com', 'http://www.michaeljackson.com', 'http://www.Australia.com', 'http://www.rafaelnadal.com', 'http://www.rogerfederer.com'], 'UK': ['http://www.uk.com']}

I want to union them i.e.

How to do it in Python without overwwriting and replacing any value?

Upvotes: 2

Views: 752

Answers (1)

mgilson
mgilson

Reputation: 310089

Use a defaultdict:

from collections import defaultdict
d  = defaultdict(list)

for dd in (a,bb):
    for k,v in dd.items():
        #Added this check to make extending work for cases where 
        #the value is a string.
        v = (v,) if isinstance(v,basestring) else v  #basestring is just str in py3k.
        d[k].extend(v)

(but this is pretty much what I told you in my earlier answer)

This now works if your input dictionaries look like 

{'Australia':['http://www.australia.com']}

or like: 

{'Australia':'http://www.australia.com'}

However, I would advise against the latter form. In general, I think it's a good idea to keep all the keys/values of a dictionary looking the same (at least if you want to treat all the items the same as in this question). That means that if one value is a list, it's a good idea for all of them to be a list.

If you really insist on keeping things this way:

d = {}
for dd in (a,b):
   for k,v in dd.items():
       if(not isinstance(v,list)):
          v = [v]
       try:
          d[k].extend(v)
       except KeyError: #no key, no problem, just add it to the dict.
          d[k] = v

Upvotes: 3

Related Questions