merging two dictionaries - Printable Version

merging two dictionaries - Printable Version

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merging two dictionaries - Skaperen - Oct-03-2017

i am looking for a way to merge, combine, or add two dictionaries. i would expect any key(s) in both would be in the result with the value from a designated dictionary (either the 1st or the 2nd).

i initially expected something like this to work:

d1 = {1:'one',2:'two'}
d2 = {2:'deux',3:'trois'}
d3 = d1 + d2

giving a result the same as:

d3 = {1:'one',2:'deux',3:'trois'}

the closest thing i could find in the documentation was the .update method. but, .update would modify its self dictionary in place and not return the result, so:

d1 = {1:'one',2:'two'}
d2 = {2:'deux',3:'trois'}
d3 = d1.update(d2)

would not work, requiring code like:

d1 = {1:'one',2:'two'}
d2 = {2:'deux',3:'trois'}
d3 = copy.copy(d1)
d3.update(d2)

but in something like function call arguments this just gets messy. any good ideas how to merge two dictionaries without creating an extra one in the code?

RE: merging two dictionaries - buran - Oct-03-2017

Doesn't this do what you want?

d3 = d1.copy().update(d2)

RE: merging two dictionaries - metulburr - Oct-03-2017

Quote:but in something like function call arguments this just gets messy. any good ideas how to merge two dictionaries without creating an extra one in the code?

put it in a function and call the function in the other functions params

RE: merging two dictionaries - buran - Oct-03-2017

(Oct-03-2017, 01:33 AM)buran Wrote: Doesn't this do what you want?
d3 = d1.copy().update(d2)

d3 = d1.copy()
d3.update(d2)

RE: merging two dictionaries - Skaperen - Oct-03-2017

i am wanting to put it in a function call and not even have d3, like:

example_function(d1+d2)

RE: merging two dictionaries - buran - Oct-03-2017

https://bugs.python.org/issue6410
Well, support for dict.__add__ has been rejected long ago

RE: merging two dictionaries - nilamo - Oct-03-2017

You can always roll your own. Just because it isn't in dict doesn't mean you can't use things that waddle and quack like dicts...

class Wrapper(dict):
    def __add__(self, other):
        final = {}
        for obj in [self, other]:
            final.update(obj)
        return final

a = Wrapper({1: 2, 3: 4})
b = Wrapper({1: 3, 5: 6})
print(a+b)
# {1: 3, 3: 4, 5: 6}

RE: merging two dictionaries - Skaperen - Oct-03-2017

i was thinking maybe i'd have to roll my own. i get that thought when i can't find it in the docs. dict add is not hard. pike has it (different terminology ... "mapping" is the direct term in pike).

so would dictmerge(a,b,...) be a good choice, or maybe dictmerge([a,b,...]), or maybe an implementation that can do it either way. or would you rather see a different name? dictjoin?

RE: merging two dictionaries - wavic - Oct-03-2017

Well, it's is a good idea in general to be created Merge class to handle all obj + obj statements for all of these types which don't have __add__ method into the type class definition.

RE: merging two dictionaries - snippsat - Oct-03-2017

>>> d1 = {1:'one',2:'two'}
>>> d2 = {2:'deux',3:'trois'}
>>> d3 = {**d1, **d2}
>>> d3
{1: 'one', 2: 'deux', 3: 'trois'}