Re: counting items

[Steven Bethard]

Mark McEahern wrote:
It's me wrote:
Okay, I give up.
What's the best way to count number of items in a list [that may 
contain lists]?
 

a = [[1,2,4],4,5,[2,3]]
def iterall(seq):
   for item in seq:
       try:
           for subitem in iterall(item):
               yield subitem
       except TypeError:
           yield item
all = [x for x in iterall(a)]
print len(all)
Beware:
py> list(iterall(['a']))
Traceback (most recent call last):
  File "<interactive input>", line 1, in ?
  File "<interactive input>", line 4, in iterall
  ...
  File "<interactive input>", line 4, in iterall
RuntimeError: maximum recursion depth exceeded
You need to special-case strings.  I would do this explicitly, e.g.:
py> def iterall(seq):
...    for item in seq:
...        if isinstance(item, basestring):
...            yield item
...        else:
...            try:
...                for subitem in iterall(item):
...                    yield subitem
...            except TypeError:
...                yield item
...
py> list(iterall(['a']))
['a']
but you can also do this by checking for __iter__ as in one of the other 
posted solutions.  (This takes advantage of the fact that strings use 
the __getitem__ protocol for iteration instead of __iter__.)

Steve
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