[Python-3000] symbols?

[Ian Bicking]

Martin v. Löwis wrote:
> Kendall Clark wrote:
> 
>>Thanks, Martin. That is, in fact, pretty much what I'd like to see in
>>Py3K, modulo the issue about getattr.
> 
> 
> The question is still: why? In Smalltalk, symbols are used to denote
> names (methods/selector names and class names); this apparently isn't
> your intention (and I do believe strings serve fine as names, no need
> for a new datatype - except that it should support Unicode).
> 
> So the only advantage I can see is the simplified typing: instead of
> typing two quotation marks, you type a single colon. It might be
> a saving on your keyboard that you don't have to press the shift key
> (is colon available unshifted on US keyboards?); I have to press
> the shift key either way (: is shift-.; " is shift-2).

Symbols make it clear you are talking about some more-constrained value 
(like an enumeration), or an in-process name (like a method name). 
Strings can just be data, which is generally used very differently.  In 
addition to immutability, I think this is an important part of how 
symbols are used in Lisp and Ruby (they don't seem to actually be used 
as much in Smalltalk, more of an implementation detail).  Also, when 
passed a string or symbol, you can get a better idea of what it was 
intended for.  And, for example, having to cast the string to a symbol 
before using it with getattr() will make the security implications a 
little clearer.

At the same time, I think it is more in line with Python's design to 
avoid talking about the names of things, and instead talk about the 
things themselves.  After all, you don't do:

   make(:var, 10)

You do:

   var = 10

In most cases this is how Python works now.  Literal strings show up 
sometimes.  I see them in descriptors (or complex tricks to avoid them). 
  In hasattr() they are common, in getattr() occasionally to make use of 
the third getattr() argument -- either can be avoided with try:except 
AttributeError: if you choose.  That's most of what I can think of now.


-- 
Ian Bicking  /  ianb at colorstudy.com  /  http://blog.ianbicking.org