[Python-3000] Making strings non-iterable

[Brian Harring]

On Mon, Apr 17, 2006 at 05:40:19PM -0500, Ian Bicking wrote:
> Raymond Hettinger wrote:
> > -1 on making strings non-iterable.  The cure is worse than the disease.  
<snip>
> > I'm also -1 on almost all proposals of this kind.  IMHO, the first cut 
> > of Py3000 should be directed at subtracting the cruft and consolidating 
> > what we have.  It should be a better Python, not just a different 
> > Python.  The surest route to that goal is to build on what has been 
> > shown to work and experiment with random alternatives that may or may 
> > not ultimately prove their worth.
> 
> I don't see how this is so dramatically different.  I proposed it
> specifically to remove something that at least I considered a language
> wart: an area prone to errors that provides an interface inconsistent
> with other parts of the language.

The issue I'm seeing is that the wart you're pointing at is a general 
issue not limited to strings- everyone sooner or later has flattening 
code that hits the "recursively iterate over this container, except 
for instances of these classes".  General algo problem for nested 
sequences.

I'd rather see a builtin that makes that case easier then to go and 
remove iteration on strings- something akin to

def iter_flatten(lists, dont_iterate=[str]):
  stack=[iter(lists)]
  while stack:
    for x in stack[-1]:
      if hasattr(x, "__iter__") and isinstance(x, dont_iterate):
          stack.append(iter(x))
          break
      yield x
    else:
      stack.pop(-1)

That (assuming I didn't typo it) addresses the issue in a general way, 
without removing (useful) __iter__ from instances that occasionally we 
don't want to fully expand.  

An easier way to invoke a func of the sort from above gets the best of 
both worlds- still have iteration over strings, and general solution 
to common problem.

Downside is that it forces an extra func call for the following if 
it's unknown if the instance is a string or a normal sequence-

for x in iter_flatten(unknown_type_instance):
  do_something_with_it(x)

~harring
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