Python merge list of dictionaries

How can I turn a list of dicts like [{'a':1}, {'b':2}, {'c':1}, {'d':2}], into a single dict like {'a':1, 'b':2, 'c':1, 'd':2}?

Answers here will overwrite keys that match between two of the input dicts, because a dict cannot have duplicate keys. If you want to collect multiple values from matching keys, see How to merge dicts, collecting values from matching keys?.

asked Aug 16, 2010 at 15:55

5

This works for dictionaries of any length:

>>> result = {}
>>> for d in L:
...    result.update[d]
... 
>>> result
{'a':1,'c':1,'b':2,'d':2}

As a comprehension:

# Python >= 2.7
{k: v for d in L for k, v in d.items[]}

# Python < 2.7
dict[pair for d in L for pair in d.items[]]

wim

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answered Aug 16, 2010 at 16:56

0

In case of Python 3.3+, there is a ChainMap collection:

>>> from collections import ChainMap
>>> a = [{'a':1},{'b':2},{'c':1},{'d':2}]
>>> dict[ChainMap[*a]]
{'b': 2, 'c': 1, 'a': 1, 'd': 2}

Also see:

• What is the purpose of collections.ChainMap?

answered Jan 13, 2016 at 5:50

alecxealecxe

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1

Little improvement for @dietbuddha answer with dictionary unpacking from PEP 448, for me, it`s more readable this way, also, it is faster as well:

from functools import reduce
result_dict = reduce[lambda a, b: {**a, **b}, list_of_dicts]

But keep in mind, this works only with Python 3.5+ versions.

answered Feb 9, 2020 at 17:09

1

This is similar to @delnan but offers the option to modify the k/v [key/value] items and I believe is more readable:

new_dict = {k:v for list_item in list_of_dicts for [k,v] in list_item.items[]}

for instance, replace k/v elems as follows:

new_dict = {str[k].replace[" ","_"]:v for list_item in list_of_dicts for [k,v] in list_item.items[]}

unpacks the k,v tuple from the dictionary .items[] generator after pulling the dict object out of the list

answered May 4, 2018 at 16:29

SchaltonSchalton

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For flat dictionaries you can do this:

from functools import reduce
reduce[lambda a, b: dict[a, **b], list_of_dicts]

SiHa

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answered Apr 16, 2013 at 22:36

dietbuddhadietbuddha

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>>> L=[{'a': 1}, {'b': 2}, {'c': 1}, {'d': 2}]    
>>> dict[i.items[][0] for i in L]
{'a': 1, 'c': 1, 'b': 2, 'd': 2}

Note: the order of 'b' and 'c' doesn't match your output because dicts are unordered

if the dicts can have more than one key/value

>>> dict[j for i in L for j in i.items[]]

answered Aug 16, 2010 at 16:38

John La RooyJohn La Rooy

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3

You can use join function from funcy library:

from funcy import join
join[list_of_dicts]

answered Jun 4, 2014 at 21:05

SuorSuor

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1

If you don't need the singleton dicts anymore:

>>> L = [{'a':1}, {'b':2}, {'c':1}, {'d':2}]
>>> dict[map[dict.popitem, L]]
{'a': 1, 'b': 2, 'c': 1, 'd': 2}

answered Oct 2, 2021 at 12:41

no commentno comment

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dict1.update[ dict2 ]

This is asymmetrical because you need to choose what to do with duplicate keys; in this case, dict2 will overwrite dict1. Exchange them for the other way.

EDIT: Ah, sorry, didn't see that.

It is possible to do this in a single expression:

>>> from itertools import chain
>>> dict[ chain[ *map[ dict.items, theDicts ] ] ]
{'a': 1, 'c': 1, 'b': 2, 'd': 2}

No credit to me for this last!

However, I'd argue that it might be more Pythonic [explicit > implicit, flat > nested ] to do this with a simple for loop. YMMV.

answered Aug 16, 2010 at 15:58

KatrielKatriel

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1

>>> dictlist = [{'a':1},{'b':2},{'c':1},{'d':2, 'e':3}]
>>> dict[kv for d in dictlist for kv in d.iteritems[]]
{'a': 1, 'c': 1, 'b': 2, 'e': 3, 'd': 2}
>>>

Note I added a second key/value pair to the last dictionary to show it works with multiple entries. Also keys from dicts later in the list will overwrite the same key from an earlier dict.

answered Aug 16, 2010 at 16:59

Dave KirbyDave Kirby

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this way worked for me:

object = [{'a':1}, {'b':2}, {'c':1}, {'d':2}]
object = {k: v for dct in object for k, v in dct.items[]}

printing object:

object = {'a':1,'b':2,'c':1,'d':2}

thanks Axes

answered Sep 26 at 13:14

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