#17958: implement declare_var, deprecate (None)var
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Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.6
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by jdemeyer:
Old description:
> Functions returning a value should not have side effects, `var` does. In
> #17447, comment 23 Nils Bruin proposed to separate both usages of `var`
> by introducing `declare_var`: this should behave exactly like `var`
> without return value, and `var` should not put the var handle in the
> `globals` list but should act like `SR.var`. If we want the following
> behaviour:
> 1. `declare_var('x')` == `var('x')` as before but returning `None`
> 2. `var('x')` prints deprecation message, returns variable as before;
> error after deprecation period
> 3. `y = var('x')` as before (but without globals), NO deprecation
> message
> we certainly need the preparser to recognize 2/3, and to replace (2) with
> `declare_var('x'); deprecation(...); x` and (3) with `y = SR.var('x')`.
> Secondly, there is a different docstring needed with `var` when compared
> with `declare_var`.
>
> This and the same with functions is the most annoying problem for people
> doing calculus in Sage.
>
> * http://ask.sagemath.org/question/8145/difference-between-varx-and-
> xvarx/
>
> Also #6559 deprecated the `ns` keyword 5 years ago, let's remove it from
> `var()`.
New description:
Functions returning a value should not have side effects, `var` does. In
#17447, comment 23 Nils Bruin proposed to separate both usages of `var` by
introducing `declare_var`: this should behave exactly like `var` without
return value, and `var` should not put the var handle in the `globals`
list but should act like `SR.var`. If we want the following behaviour:
1. `declare_var('x')` == `var('x')` as before but returning `None`
2. `var('x')` prints deprecation message, returns variable as before;
error after deprecation period
3. `y = var('x')` as before (but without globals), NO deprecation message
we certainly need the preparser to recognize 2/3, and to replace (2) with
`declare_var('x'); deprecation(...); x` and (3) with `y = SR.var('x')`.
Secondly, there is a different docstring needed with `var` when compared
with `declare_var`.
This and the same with functions is the most annoying problem for people
doing calculus in Sage.
* http://ask.sagemath.org/question/8145/difference-between-varx-and-
xvarx/
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Ticket URL: <http://trac.sagemath.org/ticket/17958#comment:44>
Sage <http://www.sagemath.org>
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