Python's dict objects can be merged :: semicomplete.com

Fri, 14 Jul 2006

Python's dict objects can be merged

Much to my surprise, python dict objects can be merged. I've needed this a few times but never knew about it mostly due to 'pydoc dict' not mentioning 'merge' anywhere.

>>> a = { 1: 2, 3: 4 }
>>> b = { 1: 100, 5: 6 }
>>> b.update(a)
>>> print b
{1: 2, 3: 4, 5: 6}

dict.update() takes any number of arguments, all of which must be dict objects. This lets you merge serveral dicts into one. Conflict resolution, it seems, is "last one in wins."

Comments: 3 (view comments)
Tags: python
Permalink: /geekery/python-dict-merging
posted at: 03:42

3 responses to 'Python's dict objects can be merged'

niffshack posted at Sat Aug 5 14:32:32 2006...

Thanks, man! Just what I needed.

Came across your blog via google, in search of just this.

It is in the documentation, but I never would have thought to look for a method named "update"...

Jim Ostrowski posted at Thu Mar 1 19:46:05 2007...

Thanks for that tidbit!! It was exactly what I needed, and the docs weren't getting me there...

na posted at Wed Jul 2 05:46:15 2008...

Consider this helper function. It does not mutate the original and works with any number of arguments.

import operator

def DictMerge(*dicts):
return dict(reduce(operator.add, [x.items() for x in dicts]))

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