Flatten a list (or list of lists, etc.) (Python recipe) by Sunjay Varma

ActiveState Code (http://code.activestate.com/recipes/577255/)

How about this?

def flatten(*args):
    for x in args:
        if hasattr(x, '__iter__'):
            for y in flatten(*x):
                yield y
        else:
            yield x

>>> list(flatten(1, 2, ['b', 'a', 'c']))
[1, 2, 'b', 'a', 'c']

I am not that familiar with the yield statement. Could you please explain further?

Sherry that's brilliant with way less code and all the goodies from generators ;) way better than other's version ...

Sunjay Varma as you can see there are always more efficient ways to code things , especially in interpreted languages , so it is not polite to criticize other people codes in that manner ... in my opinion this site supposed to be about learning and sharing not judging ...

Sorry about that. I didn't mean to seem rude. I only posted because I thought that the community would benefit from different versions of functions.

Thanks to this recipe, we now have a great generator version as well.

-Sunjay03

Just something to add, Sherry's recipe above is very good for iteration, but for list stuff, you would have to add the extra statement

list(flatten([1],23,[21],[213,1]))

Which might be inconvenient for some people.

-Sunjay03

Sorry back so late, I do not always online.

Sunjay Varma, as you see, generator is a simpler, faster and more memory efficient way(I like it ^ ^). For more information, you can read the python official documentation: http://docs.python.org/reference/simple_stmts.html#the-yield-statement.

Except generators, I used "hasattr(x, '__iter__')" instead of "isinstance(x, (list, tuple))" to check the argument can be iterative. Not only list and tuple, I hoped it also work for set, xrange(python 2.x), generator and iterator types. For example:

>>> a = 1  # int
>>> b = 'abc'  # str
>>> c = (2, 3, 4)  # tuple
>>> d = ['d', 'e', 'f']  # list
>>> e = set((5, 6))  # set
>>> f = xrange(2)  # xrange
>>> g = (i*2 for i in f)  # generator
>>> list(flatten(a, b, c, d, e, f, g))
[1, 'abc', 2, 3, 4, 'd', 'e', 'f', 5, 6, 0, 1, 0, 2]

More information: http://docs.python.org/library/stdtypes.html#built-in-types.

Lastly, I prefer to use generators if there is not necessary to get all elements and creat a list to memorize them. Maybe using a for loop is better?

>>> for i in flatten(a, b, c, d, e, f, g):
        print i,    
1 abc 2 3 4 d e f 5 6 0 1

Sorry for my poor English. Enjoy.

Thanks I agree completely. :)