On Mar 16, 2005, at 6:19, Raymond Hettinger wrote:
Some folks on comp.lang.python have been pushing for itertools to include a flatten() operation. Unless you guys have some thoughts on the subject, I'm inclined to accept the request.
Rather than calling it flatten(), it would be called "walk" and provide
a generalized capability to descend through nested iterables (similar to
what os.walk does for directories). The one wrinkle is having a
stoplist argument to specify types that should be considered atomic
eventhough they might be iterable (strings for example).
You could alternatively give them a way to supply their own "iter" function, like the code I demonstrate below:
from itertools import chain
def nostring_iter(obj):
if isinstance(obj, basestring):
raise TypeError
return iter(obj)def uniqueiter_factory(iterfunc=nostring_iter):
def uniqueiter(obj, uniques={}):
iterable = iterfunc(obj)
if id(obj) in uniques:
raise TypeError
uniques[id(obj)] = obj
return iterable
return uniqueiter# maybe there should be a bfswalk too?
def walk(iterable, iterfunc=nostring_iter):
iterables = iter((iterable,))
while True:
for obj in iterables:
try:
iterable = iterfunc(obj)
except TypeError:
yield obj
else:
iterables = chain(iterable, iterables)
break
else:
break>>> data = [('foo', 'bar'), 'baz', 5]
>>> list(walk(data))
['foo', 'bar', 'baz', 5]
>>> list(walk(data, uniqueiter_factory(iter)))
['f', 'o', 'o', 'b', 'a', 'r', 'b', 'a', 'z', 5]
>>> data.append(data)
>>> list(walk(data, uniqueiter_factory()))
['foo', 'bar', 'baz', 5, [('foo', 'bar'), 'baz', 5, [...]]]-bob
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