Re: Why no '|' operator for dict?
You can use keyword-argument unpacking in a dict-constructor.
Values of duplicate keys are overwritten from left to right. The last wins.
>>> dict1 = {'foo': 13, 'bar': 42}
>>> dict2 = {'foo': 42, 'hello': 'world'}
>>> {**dict1, **dict2}
{'bar': 42, 'foo': 42, 'hello': 'world'}
{**dict2, **dict1}
{'bar': 42, 'foo': 13, 'hello': 'world'}
You can make a Class for this task, if you need it very often:
class UDict(dict):
def __or__(self, other):
if not isinstance(other, (self.__class__, dict)):
raise ValueError('Is not a dict!')
return {**self, **other}
__ror__ = __or__
>>> UDict({'foo': 1, 'bar': 1337}) | UDict({'bar': 43})
{'bar': 43, 'foo': 1}
>>> UDict({'foo': 1, 'bar': 1337}) | {'bar': 43}
{'bar': 43, 'foo': 1}
>>> {'foo':42} | UDict({'foo': 1, 'bar': 1337})
{'bar': 1337, 'foo': 42}
Greetings
Andre
Steven D'Aprano schrieb am Mo., 5.
Feb. 2018 um 11:03 Uhr:
> On Mon, 05 Feb 2018 01:14:53 -0700, Ian Kelly wrote:
>
> > On Mon, Feb 5, 2018 at 12:35 AM, Frank Millman
> > wrote:
> >> So I have 2 questions -
> >>
> >> 1. Is there any particular reason why '|' is not supported?
> >
> > '|' is the set union operation, roughly equivalent to the set.union
> > method. Dicts don't have a union operation. If they did, and the same
> > key were found in both sets, what would be the value of that key in the
> > union?
>
> Obviously it should be a quantum superposition of the two values, which
> remains uncertain until such time as you actually print the value and
> observe it.
>
>
>
>
> --
> Steve
>
> --
> https://mail.python.org/mailman/listinfo/python-list
>
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Re: Why no '|' operator for dict?
On Mon, 05 Feb 2018 01:14:53 -0700, Ian Kelly wrote: > On Mon, Feb 5, 2018 at 12:35 AM, Frank Millman > wrote: >> So I have 2 questions - >> >> 1. Is there any particular reason why '|' is not supported? > > '|' is the set union operation, roughly equivalent to the set.union > method. Dicts don't have a union operation. If they did, and the same > key were found in both sets, what would be the value of that key in the > union? Obviously it should be a quantum superposition of the two values, which remains uncertain until such time as you actually print the value and observe it. -- Steve -- https://mail.python.org/mailman/listinfo/python-list
Re: Why no '|' operator for dict?
05.02.18 10:14, Ian Kelly пише:
On Mon, Feb 5, 2018 at 12:35 AM, Frank Millman wrote:
So I have 2 questions -
1. Is there any particular reason why '|' is not supported?
'|' is the set union operation, roughly equivalent to the set.union
method. Dicts don't have a union operation. If they did, and the same
key were found in both sets, what would be the value of that key in
the union?
2. Is there a better way to do what I want?
The dict.items() view is explicitly set-like and can be unioned, so
you can do this:
py> dict(d1.items() | d2.items())
This doesn't work with non-hashable values.
The simplest (and perhaps the most efficient) way in recent Python
versions is:
{**d1, **d2}
In old Python versions this should be written as
d = dict(d1)
d.update(d2)
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Re: Why no '|' operator for dict?
On 2/5/2018 2:35 AM, Frank Millman wrote:
I recently learned that you can create a set 'on-the-fly' from two
existing sets using the '|' operator -
Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 08:06:12) [MSC v.1900 64
bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
set_1 = set(('a', 'b', 'c'))
set_2 = set(('d',))
set_1 | set_2
{'d', 'a', 'c', 'b'}
I was hoping that I could do the same with a dictionary, but it does not
work -
If you know keys are unique or you want keep the second value for a
duplicate (equal) key,
>>> d1 = {1: 'one', 2: 'two'}; d2 = {3: 'three', 1:'One'}
>>> d3 = d1.copy()
>>> d3.update(d2)
>>> d3
{1: 'One', 2: 'two', 3: 'three'}
--
Terry Jan Reedy
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Re: Why no '|' operator for dict?
2018-02-05 9:14 GMT+01:00 Ian Kelly : > On Mon, Feb 5, 2018 at 12:35 AM, Frank Millman wrote: >> 2. Is there a better way to do what I want? > > The dict.items() view is explicitly set-like and can be unioned, so > you can do this: > > py> dict(d1.items() | d2.items()) > > As to the question of which value will appear in the union in the case > of duplicate keys, it will be whichever one arbitrarily appears later > in the iteration order of the intermediate set. Since Python 3.5, it is also possible to use PEP448 generalized unpacking: dict([*d1.items(), *d2.items()]) In which case the value that appears in case of duplicate keys is better defined, it will be the one appearing in the last dictionnary. -- https://mail.python.org/mailman/listinfo/python-list
Re: Why no '|' operator for dict?
"Ian Kelly" wrote in message news:calwzidkp3ls4s-zi3ax6no-68kw4_xdozvwa-cj+oz+apqr...@mail.gmail.com... On Mon, Feb 5, 2018 at 12:35 AM, Frank Millman wrote: > So I have 2 questions - > > 1. Is there any particular reason why '|' is not supported? '|' is the set union operation, roughly equivalent to the set.union method. Dicts don't have a union operation. If they did, and the same key were found in both sets, what would be the value of that key in the union? > 2. Is there a better way to do what I want? The dict.items() view is explicitly set-like and can be unioned, so you can do this: py> dict(d1.items() | d2.items()) Excellent explanation, and excellent solution! Thanks very much. Frank -- https://mail.python.org/mailman/listinfo/python-list
Re: Why no '|' operator for dict?
On Mon, Feb 5, 2018 at 12:35 AM, Frank Millman wrote: > So I have 2 questions - > > 1. Is there any particular reason why '|' is not supported? '|' is the set union operation, roughly equivalent to the set.union method. Dicts don't have a union operation. If they did, and the same key were found in both sets, what would be the value of that key in the union? > 2. Is there a better way to do what I want? The dict.items() view is explicitly set-like and can be unioned, so you can do this: py> dict(d1.items() | d2.items()) As to the question of which value will appear in the union in the case of duplicate keys, it will be whichever one arbitrarily appears later in the iteration order of the intermediate set. -- https://mail.python.org/mailman/listinfo/python-list
Why no '|' operator for dict?
Hi all
I recently learned that you can create a set 'on-the-fly' from two existing
sets using the '|' operator -
Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 08:06:12) [MSC v.1900 64 bit
(AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
set_1 = set(('a', 'b', 'c'))
set_2 = set(('d',))
set_1 | set_2
{'d', 'a', 'c', 'b'}
I was hoping that I could do the same with a dictionary, but it does not
work -
dict_1 = {1: 'one', 2: 'two'}
dict_2 = {3: 'three'}
dict_1 | dict_2
Traceback (most recent call last):
File "", line 1, in
TypeError: unsupported operand type(s) for |: 'dict' and 'dict'
The best that I can come up with is -
dict([(k, v) for k, v in dict_1.items()] + [(k, v) for k, v in
dict_2.items()])
{1: 'one', 2: 'two', 3: 'three'}
So I have 2 questions -
1. Is there any particular reason why '|' is not supported?
2. Is there a better way to do what I want?
Thanks
Frank Millman
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