>>> Is the syntax for this stuff set in stone? I'm not sure I like the
>>> equality inside the subs call. Equality is reflexive, but
>>> substitution is a one way operation. What about a dictionary, sage: (a
>>> +2*b).subs({a+b:x}), or even just a single equal sign, like keyword
>>> args, sage: (a+2*b).subs(a+b=x). The double equals would work too,
>>> but now is probably a better time for discussion than later.
>>
>> I am also in favor of the dictionary and/or keyword arguments (which are
>> equivalent from the programming pov). This is also the current
>> interface for other subs functions in Sage.
>>
>> I realized that William had already wrapped these functions right after
>> I wrote the message saying I'll get to it soon. Though when I tried
>> using them, I expected them to work with keyword arguments, and had to
>> look in the docs.
>>
>> I suggest we change this back to be consistent with the already
>> existing objects in Sage.
>>
>> Comments?
>
> Yes, definitely definitely change subs to take a dictionary and also **args,
> just like the current calculus subs!
>
> I think it might be good to leave in an _subs method that
> works with relationals as input. The *only* reason I implemented
> something taking relationals as input is that I was simply directly wrapping
> the
> GiNaC api as is, and doing so pretty much in autopilot after about 15 hours
> of nonstop coding. I don't think it's actually a good idea. That said,
> maybe there is some value to at least providing a direct way to use that
> function in the "GiNaC way".
Yep, sympy also uses dicts in .subs(), e.g. .subs({x: 2, y: z}) and
also .subs(old, new). It has proven very handy.
Ondrej
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