string interpolation for python

[Steven D'Aprano]

On Mon, 02 Apr 2012 00:39:42 -0700, Yingjie Lan wrote:

>> You can already do essentially that without adding a special-case
>> string
> 
>> formatting method to the general methods we already have.
>> 
>>>>>  balls = 5
>>>>>  people = 3
>>>>>  'The {people} people have {balls}
>> balls.'.format(**locals())
>> 'The 3 people have 5 balls.'
> 
> 
> Clearly dynamic strings are much more powerful, allowing arbitrary
> expressions inside.

And so it may be a security risk, if user-input somehow ends up treated 
as a dynamic string.

We already have three ways to evaluate arbitrary expressions:

* Python code
* eval
* exec

Why do we need yet another one?


> It is also more terse and readable, since we need no
> dictionary.

I think you mean terse and unreadable, since we need no dictionary. That 
means that variables will be evaluated by magic from... where? Globals? 
Local scope? Non-local scope? All of the above?

We already have one way of evaluating implicit variables using implicit 
rules, namely regular Python code. Why do we need a second one?


> I would probably rather liken dynamic expressions as a little brother of
> computable documents in Mathematica. It is a new kind of expression,
> rather than formatting -- though it has formatting connections.

Why do we need a new kind of expression?


> Dynamic strings are mainly useful at time of writing readable code
> before compilation.

What does that mean?


> The compiler can choose to convert it into a string
> formatting expression, of course. To efficiently format strings at
> runtime, the best choice (especially
> for safty reasons) is string formatting, not evaluating a dynamic
> string.

So you're suggesting that we should have dynamic strings, but not 
actually use dynamic strings. The compiler should just convert them to 
regular string formatting.

Why not cut out the middle-man and just use regular string formatting?



-- 
Steven