# Flatten a nested list of lists

[Making a flat list out of list of lists in Python - Stack Overflow](https://stackoverflow.com/questions/952914/making-a-flat-list-out-of-list-of-lists-in-python#45323085)

**Example:**

\[\[1, 2, 3], \[4, 5, 6], \[7], \[8, 9]]

```python
import functools
import itertools
import numpy
import operator
import perfplot


def forfor(a):
    return [item for sublist in a for item in sublist]


def sum_brackets(a):
    return sum(a, [])


def functools_reduce(a):
    return functools.reduce(operator.concat, a)


def itertools_chain(a):
    return list(itertools.chain.from_iterable(a))


def numpy_flat(a):
    return list(numpy.array(a).flat)


def numpy_concatenate(a):
    return list(numpy.concatenate(a))


perfplot.show(
    setup=lambda n: [list(range(10))] * n,
    kernels=[
        forfor, sum_brackets, functools_reduce, itertools_chain, numpy_flat,
        numpy_concatenate
        ],
    n_range=[2**k for k in range(16)],
    logx=True,
    logy=True,
    xlabel='num lists'
    )
```


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