Question

I edited it. I made them lists to dictionaries. 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 union them

{'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?**

Answer 1

Consider using a different data structure, such as a dictionary of sets.

a = [['UK', ['http://www.uk.com']], ['COM', ['http://www.uk.com'],['http://www.michaeljackson.com']]]
b = [['Australia', ['http://www.australia.com']], ['COM', ['http://www.Australia.com'], ['http://www.rafaelnadal.com'], ['http://www.rogerfederer.com']]]

# convert these to dictionaries with set values
a = {item[0]:set(s[0] for s in item[1:]) for item in a}
b = {item[0]:set(s[0] for s in item[1:]) for item in b}

# define a function to update our dictionary-of-sets data structure
def union_update_setdict(D, *setdicts):
    """Update dictionary D (with `'key':set(value)` items) with items from setdicts.

    If a new key is added to D from setdicts, a shallow copy of the value
    is added to D.
    """
    for setdict in setdicts:
        for k,v in setdict.items():
            try:
                D[k].update(v)
            except KeyError:
                D[k] = v.copy()

union_update_setdict(a, b)



# Now let's test that the code works

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

# put the "expected" results in our new data structure for comparison
expected = {item[0]:set(s[0] for s in item[1:]) for item in expected}

print a
assert expected == a

If you really need to keep using your terrible data structure, you can convert it back when you are finished:

terribledatastruct = [[k]+[[item] for item in v] for k,v in a.items()]
print terribledatastruct