[Python-3000] Making strings non-iterable

[Nick Coghlan]

Barry Warsaw wrote:
> On Wed, 2006-04-19 at 20:17 +1000, Nick Coghlan wrote:
> 
>> Unfortunately, the thread fizzled without generating any additional interest. 
>> I don't recall the topic really coming up since then.
> 
> Maybe because the proposal got too complex while trying to be so
> general?

One way to simplify it would be to special case strings rather than provide a 
general stop list (this would be significantly simpler to do in C, too):

from itertools import chain

def walk(iterable, depth_first=True, iter_strings=False):
    itr = iter(iterable)
    while True:
      for item in itr:
        if isinstance(item, basestring):
          # We have a string
          # Don't iterate if flag is not set
          # Never iterate if length is only 1
          if not iter_strings or len(item) == 1:
              yield item
              continue
        try:
          subitr = iter(item)
        except TypeError:
          yield item
          continue
        if depth_first:
            itr = chain(subitr, itr)
        else:
            itr = chain(itr, subitr)
        break # Restart the inner for loop
      else:
        break # Finish the outer while loop

Py> seq = [['123', '456'], 'abc', 'abc', 'abc', 'abc', ['xyz']]
Py> seq
[['123', '456'], 'abc', 'abc', 'abc', 'abc', ['xyz']]
Py> list(walk(seq))
['123', '456', 'abc', 'abc', 'abc', 'abc', 'xyz']
Py> list(walk(seq, iter_strings=True))
['1', '2', '3', '4', '5', '6', 'a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c', 
'a', 'b', 'c', 'x', 'y', 'z']
Py> list(walk(seq, depth_first=False))
['abc', 'abc', 'abc', 'abc', '123', '456', 'xyz']
Py> list(walk(seq, depth_first=False, iter_strings=True))
['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c', '1', '2', '3', 
'4', '5', '6', 'x', 'y', 'z']

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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