Re: Is there a way to implement the ** operator on a custom object
On 09Feb2024 18:56, Left Right wrote: But, more to the point: extending collections.abc.Mapping may or may not be possible in OP's case. We don't yet know if that's what the OP had in mind yet, anyway. Also, if you are doing this through inheritance, this seems really convoluted: why not just inherit from dict? -- less methods to implement, less stuff to import etc. There's a rule of thumb that we _tend_ not to subclass the builtins; it certainly has its pitfalls to do with object creation/initialisation. That said, I have some classes which subclass dict, int, str and namedtuple. Cheers, Cameron Simpson -- https://mail.python.org/mailman/listinfo/python-list
Re: Is there a way to implement the ** operator on a custom object
> Looks like it can simply be done in Python, no tp_as_mapping needed. It's not that it isn't needed. You've just shown a way to add it using Python code. But, more to the point: extending collections.abc.Mapping may or may not be possible in OP's case. Also, if you are doing this through inheritance, this seems really convoluted: why not just inherit from dict? -- less methods to implement, less stuff to import etc. -- https://mail.python.org/mailman/listinfo/python-list
Re: Is there a way to implement the ** operator on a custom object
Left Right via Python-list schreef op 9/02/2024 om 17:09:
In order for the "splat" operator to work, the type of the object must
populate slot `tp_as_mapping` with a struct of this type:
https://docs.python.org/3/c-api/typeobj.html#c.PyMappingMethods and
have some non-null implementations of the methods this struct is
supposed to contain.
I can do this in C, but I cannot think of a way to do this in Python
proper.
Looks like it can simply be done in Python, no tp_as_mapping needed. I
tried it like Alan Bawden suggested (sibling post of yours):
import random # just as an example
import time # just as an example
from collections.abc import Mapping
class VirtualKwargs(Mapping):
def __init__(self):
self.fncs = {
# Simple examples of functions with varying return values to be
# called for each lookup, instead of fixed values.
'time': time.time,
'random': random.random,
}
def __len__(self):
return len(self.fncs)
def __iter__(self):
return iter(self.fncs)
def __getitem__(self, key):
return self.fncs[key]()
def func(**kwargs):
for k, v in kwargs.items():
print(f'{k}: {v}')
obj = VirtualKwargs()
func(**obj)
Output (obviously changes every run):
time: 1707497521.175763
random: 0.6765831287385126
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Re: Is there a way to implement the ** operator on a custom object
In order for the "splat" operator to work, the type of the object must populate slot `tp_as_mapping` with a struct of this type: https://docs.python.org/3/c-api/typeobj.html#c.PyMappingMethods and have some non-null implementations of the methods this struct is supposed to contain. I can do this in C, but I cannot think of a way to do this in Python proper. Defining all the methods mentioned in PyMappingMethods doesn't seem to do it. You could try to research this further, and if, indeed defining all the methods of PyMappingMethods on the Python side doesn't produce an object that behaves like a proper mapping, you could probably file a bug report for that. -- https://mail.python.org/mailman/listinfo/python-list
Re: Is there a way to implement the ** operator on a custom object
Chris Angelico writes: > On 08Feb2024 12:21, tony.fl...@btinternet.com wrote: > >I know that mappings by default support the ** operator, to unpack the > >mapping into key word arguments. > > > >Has it been considered implementing a dunder method for the ** > >operator so you could unpack an object into a key word argument, and > >the developer could choose which keywords would be generated (or could > >even generate 'virtual' attributes). I presume this is more like: obj = SomeObject() func(**obj) ie making the object behave in a dict-like way. I can't remember how this is implemented, but you can create the necessary methods to have your object produce whatever it likes. All you need to do is subclass collections.abc.Mapping, and implement __len__, __iter__, and __getitem__. Pretty easy. - Alan -- https://mail.python.org/mailman/listinfo/python-list
Re: Is there a way to implement the ** operator on a custom object
On Fri, 9 Feb 2024 at 17:03, Cameron Simpson via Python-list wrote: > > On 08Feb2024 12:21, tony.fl...@btinternet.com > wrote: > >I know that mappings by default support the ** operator, to unpack the > >mapping into key word arguments. > > > >Has it been considered implementing a dunder method for the ** > >operator so you could unpack an object into a key word argument, and > >the developer could choose which keywords would be generated (or could > >even generate 'virtual' attributes). > > Can you show us why you think that would look like in code? > > Note that Python already has `a ** b` to raise `a` to the power of `b`, > and it has a bunder method `__pow__` which you can define. I presume this is more like: obj = SomeObject() func(**obj) ie making the object behave in a dict-like way. I can't remember how this is implemented, but you can create the necessary methods to have your object produce whatever it likes. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Is there a way to implement the ** operator on a custom object
On 08Feb2024 12:21, tony.fl...@btinternet.com wrote: I know that mappings by default support the ** operator, to unpack the mapping into key word arguments. Has it been considered implementing a dunder method for the ** operator so you could unpack an object into a key word argument, and the developer could choose which keywords would be generated (or could even generate 'virtual' attributes). Can you show us why you think that would look like in code? Note that Python already has `a ** b` to raise `a` to the power of `b`, and it has a bunder method `__pow__` which you can define. -- https://mail.python.org/mailman/listinfo/python-list
Is there a way to implement the ** operator on a custom object
I know that mappings by default support the ** operator, to unpack the mapping into key word arguments. Has it been considered implementing a dunder method for the ** operator so you could unpack an object into a key word argument, and the developer could choose which keywords would be generated (or could even generate 'virtual' attributes). -- Anthony Flury email : anthony.fl...@btinternet.com -- https://mail.python.org/mailman/listinfo/python-list
