Python 3.6 merge dictionaries

John D K -

In this post:

  • Python 3.6 how to merge several dictionaries
  • Python merge dictionaries (before 3.5)
  • Python 2 merge dictionaries
  • Python 2 merge dictionaries with itertools
  • Merge of dictionaries with repetition of keys

You can check also : Python loop dictionary keys and values

Python 3.6 how to merge several dictionaries

Since python 3.5 you can use this syntax to merge two or more dictionaries(it's the fastest one):

merge = {**one, **two, **three}

Example of merging 3 dictionaries:

dictOne = {1: 'Python', 2: 'Java', 3: 'Javascript', 0:'None'}
dictTwo = {4: 'C#', 5: 'C++', 6: 'Cobol', 7:'Ruby'}
dictThree = {8: 'HTML', 9: 'CSS'}

dictMerge = {**dictOne, **dictTwo, **dictThree}

for k, v in dictMerge.items():
    print(k,  v)

result:

0 None
1 Python
2 Java
3 Javascript
4 C#
5 C++
6 Cobol
7 Ruby
8 HTML
9 CSS

Python merge dictionaries (before 3.5)

For older version this code can simulate merging of dictionaries:

dictMerge = dictOne.copy()
dictMerge.update(dictTwo)
dictMerge.update(dictThree)

Example of merging 3 dictionaries:

dictOne = {1: 'Python', 2: 'Java', 3: 'Javascript', 0:'None'}
dictTwo = {4: 'C#', 5: 'C++', 6: 'Cobol', 7:'Ruby'}
dictThree = {8: 'HTML', 9: 'CSS'}

dictMerge = dictOne.copy()
dictMerge.update(dictTwo)
dictMerge.update(dictThree)

for k, v in dictMerge.items():
    print(k,  v)

result:

0 None
1 Python
2 Java
3 Javascript
4 C#
5 C++
6 Cobol
7 Ruby
8 HTML
9 CSS

Python 2 merge dictionaries

For Python 2 merging is done by:

dictMerge = dict(dictOne.items() + dictTwo.items() + dictThree.items())

Example of merging 3 dictionaries:

dictOne = {1: 'Python', 2: 'Java', 3: 'Javascript', 0:'None'}
dictTwo = {4: 'C#', 5: 'C++', 6: 'Cobol', 7:'Ruby'}
dictThree = {8: 'HTML', 9: 'CSS'}

dictMerge = dict(dictOne.items() + dictTwo.items() + dictThree.items())

for k, v in dictMerge.items():
    print(k,  v)

result:

0 None
1 Python
2 Java
3 Javascript
4 C#
5 C++
6 Cobol
7 Ruby
8 HTML
9 CSS

Python 2 merge dictionaries with itertools

Another way to merge dictionaries in python 2 is with itertools(it's faster than previous one):

dictMerge = dict(itertools.chain(dictOne.iteritems(), dictTwo.iteritems(), dictThree.iteritems()))

Example of merging 3 dictionaries:

import itertools

dictOne = {1: 'Python', 2: 'Java', 3: 'Javascript', 0:'None'}
dictTwo = {4: 'C#', 5: 'C++', 6: 'Cobol', 7:'Ruby'}
dictThree = {8: 'HTML', 9: 'CSS'}

dictMerge = dict(itertools.chain(dictOne.iteritems(), dictTwo.iteritems(), dictThree.iteritems()))

for k, v in dictMerge.items():
    print(k,  v)

result:

0 None
1 Python
2 Java
3 Javascript
4 C#
5 C++
6 Cobol
7 Ruby
8 HTML
9 CSS

Merge of dictionaries with repetition of keys

note that in case of repetition of keys only one will be present in the merge:

dictOne = {1: 'Python', 2: 'Java', 3: 'Javascript', 0:'None'}
dictTwo = {1: 'C#', 2: 'C++', 4: 'Cobol', 0:'Ruby'}
dictMerge = {**dictOne, **dictTwo}

result:

0 Ruby
1 C#
2 C++
3 Javascript