Revisions to How do I merge two dictionaries in a single expression in Python?

Update for 3.9

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edited Dec 11, 2020 at 6:43

223.3k
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In Python 3.0 and later, you can use collections.ChainMap which groups multiple dicts or other mappings together to create a single, updateable view:

>>> from collections import ChainMap
>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> z = dict(ChainMap({}, y, x))
>>> for k, v in z.items():
        print(k, '-->', v)
    
a --> 1
b --> 10
c --> 11

Update for Python 3.5 and later: You can use PEP 448 extended dictionary packing and unpacking. This is fast and easy:

>>> x = {'a':1, 'b': 2}
>>> y = y = {'b':10, 'c': 11}
>>> {**x, **y}
{'a': 1, 'b': 10, 'c': 11}

Update for Python 3.9 and later: You can use the PEP 584 union operator:

>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> x | y
{'a': 1, 'b': 10, 'c': 11}

In Python 3.0 and later, you can use collections.ChainMap which groups multiple dicts or other mappings together to create a single, updateable view:

>>> from collections import ChainMap
>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> z = dict(ChainMap({}, y, x))
>>> for k, v in z.items():
        print(k, '-->', v)
    
a --> 1
b --> 10
c --> 11

Update for Python 3.5 and later: You can use PEP 448 extended dictionary packing and unpacking. This is fast and easy:

>>> x = {'a':1, 'b': 2}
>>> y = y = {'b':10, 'c': 11}
>>> {**x, **y}
{'a': 1, 'b': 10, 'c': 11}

In Python 3.0 and later, you can use collections.ChainMap which groups multiple dicts or other mappings together to create a single, updateable view:

>>> from collections import ChainMap
>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> z = dict(ChainMap({}, y, x))
>>> for k, v in z.items():
        print(k, '-->', v)
    
a --> 1
b --> 10
c --> 11

Update for Python 3.5 and later: You can use PEP 448 extended dictionary packing and unpacking. This is fast and easy:

>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> {**x, **y}
{'a': 1, 'b': 10, 'c': 11}

Update for Python 3.9 and later: You can use the PEP 584 union operator:

>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> x | y
{'a': 1, 'b': 10, 'c': 11}

Correction in the code. You have to explicity convert the returned ChainMap to dict to be able to iterate over it like dict.

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edited Apr 22, 2020 at 12:46

Ravindra S

6.4k
12
72
109

In Python 3.0 and later, you can use collections.ChainMap which groups multiple dicts or other mappings together to create a single, updateable view:

>>> from collections import ChainMap
>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> z = dict(ChainMap({}, y, x))
>>> for k, v in z.items():
        print(k, '-->', v)
    
a --> 1
b --> 10
c --> 11

Update for Python 3.5 and later: You can use PEP 448 extended dictionary packing and unpacking. This is fast and easy:

>>> x = {'a':1, 'b': 2}
>>> y = y = {'b':10, 'c': 11}
>>> {**x, **y}
{'a': 1, 'b': 10, 'c': 11}

In Python 3.0 and later, you can use collections.ChainMap which groups multiple dicts or other mappings together to create a single, updateable view:

>>> from collections import ChainMap
>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> z = ChainMap({}, y, x)
>>> for k, v in z.items():
        print(k, '-->', v)
    
a --> 1
b --> 10
c --> 11

Update for Python 3.5 and later: You can use PEP 448 extended dictionary packing and unpacking. This is fast and easy:

>>> x = {'a':1, 'b': 2}
>>> y = y = {'b':10, 'c': 11}
>>> {**x, **y}
{'a': 1, 'b': 10, 'c': 11}

In Python 3.0 and later, you can use collections.ChainMap which groups multiple dicts or other mappings together to create a single, updateable view:

>>> from collections import ChainMap
>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> z = dict(ChainMap({}, y, x))
>>> for k, v in z.items():
        print(k, '-->', v)
    
a --> 1
b --> 10
c --> 11

Update for Python 3.5 and later: You can use PEP 448 extended dictionary packing and unpacking. This is fast and easy:

>>> x = {'a':1, 'b': 2}
>>> y = y = {'b':10, 'c': 11}
>>> {**x, **y}
{'a': 1, 'b': 10, 'c': 11}

edited body

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edited Nov 20, 2019 at 17:03

Neuron

5.6k
5
42
61

In Python 3.0 and later, you can use collections.ChainMapcollections.ChainMap which groups multiple dicts or other mappings together to create a single, updateable view:

>>> from collections import ChainMap
>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> z = ChainMap({}, y, x)
>>> for k, v in z.items():
        print(k, '-->', v)
    
a --> 1
b --> 10
c --> 11

Update for Python 3.5 and later: You can use PEP 448 extended dictionary packing and unpacking. This is fast and easy:

>>> x = {'a':1, 'b': 2}
>>> y = y = {'b':10, 'c': 11}
>>> {**x, **y}
{'a': 1, 'b': 10, 'c': 11}

In Python 3.0 and later, you can use collections.ChainMap which groups multiple dicts or other mappings together to create a single, updateable view:

>>> from collections import ChainMap
>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> z = ChainMap({}, y, x)
>>> for k, v in z.items():
        print(k, '-->', v)
    
a --> 1
b --> 10
c --> 11

Update for Python 3.5 and later: You can use PEP 448 extended dictionary packing and unpacking. This is fast and easy:

>>> x = {'a':1, 'b': 2}
>>> y = y = {'b':10, 'c': 11}
>>> {**x, **y}
{'a': 1, 'b': 10, 'c': 11}

In Python 3.0 and later, you can use collections.ChainMap which groups multiple dicts or other mappings together to create a single, updateable view:

>>> from collections import ChainMap
>>> x = {'a':1, 'b': 2}
>>> y = {'b':10, 'c': 11}
>>> z = ChainMap({}, y, x)
>>> for k, v in z.items():
        print(k, '-->', v)
    
a --> 1
b --> 10
c --> 11

Update for Python 3.5 and later: You can use PEP 448 extended dictionary packing and unpacking. This is fast and easy:

>>> x = {'a':1, 'b': 2}
>>> y = y = {'b':10, 'c': 11}
>>> {**x, **y}
{'a': 1, 'b': 10, 'c': 11}

Add Python 3.5 update

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edited Sep 9, 2019 at 15:09

Raymond Hettinger

223.3k
65
397
494

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Make *z* independent of *x* and *y*.

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edited Sep 27, 2014 at 8:12

Raymond Hettinger

223.3k
65
397
494

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Source Link

created Apr 28, 2013 at 3:15

Raymond Hettinger

223.3k
65
397
494

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