[Python-Dev] Adding concat function to itertools (original) (raw)

Raymond Hettinger python at rcn.com
Fri Sep 28 23:53:42 CEST 2007

[Bruce Frederiksen]

I've added a new function to itertools called 'concat'. This function is much like chain, but takes all of the iterables as a single argument.

[Raymond]

Any practical use cases or is this just a theoretical improvement?

For Py2.x, I'm not willing to unnecessarily expand the module. However, for Py3k, I'm open to changing the signature for chain().

[Bruce]

For me, a fraction of chain() uses are of the * variety:

d = defaultdict(list) allvals = chain(*d.values()) return chain(*imap(cache.getitem, keylist)) Interestingly, they seem to all have something to do with dictionary values() that are themselves iterable.

I see. These are instances of a recurring general use case of chain() as a one-level flattener.

Will give consideration to changing the signature of chain() for Py3.0. Besides the concat() variation using a single iterable input, another alternative is the min()/max() style signature where one input is interpreted as iterable and multiple arguments as comprising an input tuple.

Raymond

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