How to flatten a list with various data types (int, tuple)

Question

Say I have a list with one or more tuples in it:

[0, 2, (1, 2), 5, 2, (3, 5)]

What's the best way to get rid of the tuples so that it's just an int list?

[0, 2, 1, 2, 5, 2, 3, 5]

Answer 1

One of solutions (using itertools.chain):

>>> from itertools import chain
>>> l = [0, 2, (1, 2), 5, 2, (3, 5)]
>>> list(chain(*(i if isinstance(i, tuple) else (i,) for i in l)))
[0, 2, 1, 2, 5, 2, 3, 5]

Answer 2

Using a nested list comprehension:

>>> lst = [0, 2, (1, 2), 5, 2, (3, 5)]
>>> [y for x in lst for y in (x if isinstance(x, tuple) else (x,))]
[0, 2, 1, 2, 5, 2, 3, 5]

Answer 3

def untuppleList(lst):
    def untuppleList2(x):
        if isinstance(x, tuple):
            return list(x)
        else:
            return [x]
    return [y for x in lst for y in untuppleList2(x)]

Then you can do untuppleList([0, 2, (1, 2), 5, 2, (3, 5)]).

Answer 4

A more general recursive solution, that should apply to any iterable (except strings) and any depth of elements:

import collections

def flatten(iterable):
    results = []
    for i in iterable:
        if isinstance(i, collections.Iterable) and not isinstance(i, basestring):
            results.extend(flatten(i))
        else:
            results.append(i)
    return results

And usage:

>>> flatten((1, 2, (3, 4), ('happy')))
[1, 2, 3, 4, 'happy']
>>> flatten((1, 2, (3, 4, (5, 6)), ('happy'), {'foo': 'bar', 'baz': 123}))
[1, 2, 3, 4, 5, 6, 'happy', 'foo', 'baz']

Answer 5

You can use flatten function from my funcy library:

from funcy import flatten
flat_list = flatten(your_list)

You can also peek at its implementation.