Sorry, there is no way to leverage the implementation or syntax of := for this purpose. You must be misunderstanding how they it works.
You are right that the initial value of the variable at the call site is irrelevant (but there must be some initial value, e.g. None, to be able to identify the variable). Surely there are other ways to deal with the UX problem you indicate (e.g. namedtuple). --Guido On Mon, Aug 26, 2019 at 8:33 AM HUANG YUWEI <[email protected]> wrote: > Dear Mr. Guido and Mr. Spealman, > > Thanks for your quick reply. > > Yes, something like "Out Parameters in C#" is exactly what I mentioned. > > "calling by reference" is very close, except that > - with "calling by reference", the object is initialized before the > function is called, and then being passed to function and modified. > - in my idea, the object is initialized (created) inside a function, and > its pointer (or reference) is passed to a variable X as the initialization > of variable X. > The point is that, the returned value may not have fixed type or array > shape due to the possible existence of "if condition" inside the function. > On the other hand, "calling by reference" fixes these attributes of > returned variable. > > And also you are right, this could be easily solved by returning a tuple > of multiple values, and the users just pick the returned value they need. > For low level function, the number of return variables may be 1 or 2; For > high level function which comprises of multiple low level functions, the > number of return variables could be many. Then it would look like > ``` > res0, res1, res2, res3, res4, res5, res6, res7, ..., resN = > high_level_function() > ``` > or > ``` > results = high_level_function() > res0 = results[0] > res1 = results[1] > ... > ``` > This hurts the readability of code sometimes. > > My idea is simply that, okay we are now able to have assign operator in > large expression, then why not in a function calling statement. (if the > implementation is not difficult ...) > > best regards, > Huang Y.W > > Calvin Spealman <[email protected]> 于2019年8月27日周二 上午12:00写道： > >> This also looks a lot like Out Parameters in C# ( >> https://www.c-sharpcorner.com/article/out-parameter-in-c-sharp-7/) >> >> They have a similar dichotomy of declaration and call time semantics >> using the `out` keyword rather than an assignment operator. >> >> On Mon, Aug 26, 2019 at 10:50 AM Guido van Rossum <[email protected]> >> wrote: >> >>> I think you're talking about call-by-reference (Google it). >>> >>> What would be your use case? >>> >>> Do you know you can return multiple values from a function using a >>> tuple? E.g. >>> >>> def foo(): >>> return 3, 42 >>> >>> x, y = foo() >>> print(x) # 3 >>> print(y) # 42 >>> >>> --Guido >>> >>> On Mon, Aug 26, 2019 at 5:57 AM HUANG YUWEI <[email protected]> >>> wrote: >>> >>>> Dear Python community, >>>> >>>> I am a heavy python user in numerical simulation. >>>> >>>> In python 3.8, we will have a new syntax `:=` that could assign values >>>> to variables as part of larger expression like, >>>> >>>> ``` >>>> >>>> if (n:=len(a)) > 10: >>>> >>>> .... >>>> >>>> ``` >>>> >>>> On the other hand, I also think that it would be useful if `:=` could >>>> be used in function argument, so that a local variable created inside a >>>> function could be returned **optionally**, for example, >>>> >>>> ``` >>>> >>>> def func(arg1, arg2, karg1=karg1_default, karg_return:=karg_return): >>>> >>>> ... >>>> >>>> karg_return = 3 >>>> >>>> ... >>>> >>>> return func_output >>>> >>>> >>>> # normal calling of func() without returning variable karg_return >>>> >>>> # in this way, karg_return:=karg_return is not used and karg_return is >>>> only simply a local variable in func() >>>> >>>> output = func(2,3,karg1=4) >>>> >>>> >>>> # calling func() with using the karg_return argument >>>> >>>> # in this way, value of the local variable karg_return in func() is >>>> created and "passed" to variable a >>>> >>>> output = func(2,3,karg1=4,a:=karg_return) >>>> >>>> print(a) # a = 3 >>>> >>>> ``` >>>> >>>> >>>> Is it possible to add this new feature? >>>> >>>> >>>> Thanks for your attention to this matter. >>>> >>>> Huang Y.W. >>>> _______________________________________________ >>>> Python-ideas mailing list -- [email protected] >>>> To unsubscribe send an email to [email protected] >>>> https://mail.python.org/mailman3/lists/python-ideas.python.org/ >>>> Message archived at >>>> https://mail.python.org/archives/list/[email protected]/message/ZN5XM5MSHAAN4U3VBAEBXUJB4ZUN6SUP/ >>>> Code of Conduct: http://python.org/psf/codeofconduct/ >>>> >>> >>> >>> -- >>> --Guido van Rossum (python.org/~guido) >>> *Pronouns: he/him/his **(why is my pronoun here?)* >>> <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/> >>> _______________________________________________ >>> Python-ideas mailing list -- [email protected] >>> To unsubscribe send an email to [email protected] >>> https://mail.python.org/mailman3/lists/python-ideas.python.org/ >>> Message archived at >>> https://mail.python.org/archives/list/[email protected]/message/RLHDDJ5CS77BWH6INCHPRR6UHEEHRGU4/ >>> Code of Conduct: http://python.org/psf/codeofconduct/ >>> >> >> >> -- >> >> CALVIN SPEALMAN >> >> SENIOR QUALITY ENGINEER >> >> [email protected] M: +1.336.210.5107 >> [image: https://red.ht/sig] <https://red.ht/sig> >> TRIED. TESTED. TRUSTED. <https://redhat.com/trusted> >> > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him/his **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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