Flattening an arbitrarily deep list (or any iterator) (Python)

2012-04-03T17:13:35-07:00

Python recipe 578092 by Garrett (flatten, iterator, itertools, list, python, tuple). Revision 6.

What if you had a list like this: [1, -10, [1,2,[3,4]], xrange(200)], and you just wanted to go through each element in order (wanted it to return a simple list of [1,-10,1,2,3,4,1,2,3,4...199])

I've seen a couple of attempts to flatten arbitrarily deep lists. Many of them involve recursion, like this one: http://rightfootin.blogspot.com/2006/09/more-on-python-flatten.html

Recursion is generally considered non-pythonic (at least to my knowledge), so I have used one which just involves simple iterators instead. Also, recursion will fail if the list is too deep (so it wouldn't really be arbitrary, would it?).

And yet another round-robin generator (Python)

2013-11-13T19:30:29-08:00

Python recipe 578768 by Jan Müller (generator, itertools, python, roundrobin).

I know that there is a nice recipe already that even made it into the Python documentation, but this one is more concise and at the same time simpler.

>>> list(roundrobin('ABC', 'D', 'EF'))
['A', 'D', 'E', 'B', 'F', 'C']

Yet another roundrobin (Python)

2010-07-19T13:53:41-07:00

Python recipe 577309 by Daniel Cohn (collections, itertools, roundrobin). Revision 2.

This recipe provides a decently simple implementation of a roundrobin using itertools and deque.

lazy ordered unique elements from an iterator (Python)

2011-06-23T16:36:38-07:00

Python recipe 577768 by Andrew Dalke (iterator, itertools, unique). Revision 2.

This implements a "unique" filter. Its input is an iterator of hashable items. It returns an iterator containing only the unique items of the input, in input order. That is, list(unique("cabbage")) produces ["c", "a", "b", "g"]. The implementation is lazy. The function supports the "key" parameter, which provides an alternate form of comparison.

(Note: a better version of this is available from the itertools documentation as unique_everseen )

Flattened List (Python)

2009-04-27T18:41:21-07:00

Python recipe 576719 by marlonamor (flat, generator, itertools, list, nested). Revision 2.

This flattenizes any nested level list. I couln't find this in itertools module so I wrote it. Python 3 may be required.

Recursively defined, Haskell-style infinite lists (Python)

2012-05-04T14:09:14-07:00

Python recipe 578119 by John Crichton (decorator, functional, generator, infinite, itertools, lazy, recursive). Revision 2.

A decorator to simplify the creation of recursively defined, Haskell-style infinite lists -- ie. recursive generators -- inspired by Raymond Hettinger's "Technique for cyclical iteration" [*].

[*] http://code.activestate.com/recipes/576961-technique-for-cyclical-iteration/

Iterator Offsetter (Python)

2012-04-16T13:08:55-07:00

Python recipe 577852 by Josh Bode (iterable, itertools, offset). Revision 2.

Produces a list of copies of an iterable that are offset by the supplied offsets.