How to flatten a tuple in python

Question

I have the following element of a list, and the list is 100 elements long.

[(50, (2.7387451803816479e-13, 219))]

How do I convert each element to look like this?

[(50, 2.7387451803816479e-13, 219)]

Answer 1

[(a, b, c) for a, (b, c) in l]

Tuple packing and unpacking solves the problem.

Answer 2

New in Python 3.5 with the additional tuple unpacking introduced in PEP 448, you can use starred expressions in tuple literals such that you can use

>>> l = [(50, (2.7387451803816479e-13, 219)), (40, (3.4587451803816479e-13, 220))]
>>> [(a, *rest) for a, rest in l]
[(50, 2.738745180381648e-13, 219), (40, 3.458745180381648e-13, 220)]

This could be useful if you had a nested tuple used for record-keeping with many elements that you wanted to flatten.

Answer 3

Your could use the following function and apply it in a loop to every element in the list.

def flatten(data):
    if isinstance(data, tuple):
        if len(data) == 0:
            return ()
        else:
            return flatten(data[0]) + flatten(data[1:])
    else:
        return (data,)

How it works:

• First it will be checked if type is tuple, if not, it "tuples" the argument
• Second line returns an empty tuple, if tuple is empty
• Third line gets out the first element and calls the function recursively

The nice thing in this solution is:

• It is not necessary to know the structure of the given tuple
• The tuple can be nested arbitrarily deep
• Works in Python 2.2+ (and probably earlier)

The code is slightly adapted from following source:
https://mail.python.org/pipermail/tutor/2001-April/005025.html

Hope it helps someone :)

Answer 4

An improvement from @sagacity answer, this will rerun a generator that flattens the tuple using a recursive and yield.

def flatten(data):
    if isinstance(data, tuple):
        for x in data:
            yield from flatten(x)
    else:
        yield data

To make it into list or tuple, use list() or tuple().

list(flatten(nested_tuple))
tuple(flatten(nested_tuple))

If it needs to work in Python 2, replace the yield from with another loop:

def flatten(data):
    if isinstance(data, tuple):
        for x in data:
            for y in flatten(x):
                yield y
    else:
        yield data

Answer 5

You can get the result in this way

>> example =  [(50, (2.7387451803816479e-13, 219))]
>>> [tuple(x[:1]) + (x[1]) for x in example] 
[(50, 2.738745180381648e-13, 219)]

Answer 6

A Python 2.7 compatible way to do what Mitch suggests for Python 3.5.

>>> example =  [(50, (2.7387451803816479e-13, 219)),
            (100, (3.7387451803816479e-13, 218))]
>>> [(lambda *x: x)(k, *r) for k, r in example]
[(50, 2.738745180381648e-13, 219), (100, 3.7387451803816477e-13, 218)]

The advantage of this method is that you do not have to find a variable name for each value of the internal tuple to flatten like in the accepted answer. If there are two or three items, that's not really an issue, but imagine there are tenths values or more...

Answer 7

This code works for nested tuples:

def flatten(args):
    try:
        iter(args)
        final = []
        for arg in args:
            final += flatten(arg)
        return tuple(final)
    except TypeError:
        return (args, )

flatten([1, 2, 3, 4])  # (1, 2, 3, 4)
flatten([1, [2, 3], 4])  # (1, 2, 3, 4)
flatten([1, [2, [3]], [[4]]])  # (1, 2, 3, 4)