"""
This module contains essential stuff that should've come with Python itself ;)
"""
import os
import re
import inspect
import weakref
import errno
import six
from functools import partial, wraps

from scrapy.utils.decorators import deprecated


def flatten(x):
    """flatten(sequence) -> list

    Returns a single, flat list which contains all elements retrieved
    from the sequence and all recursively contained sub-sequences
    (iterables).

    Examples:
    >>> [1, 2, [3,4], (5,6)]
    [1, 2, [3, 4], (5, 6)]
    >>> flatten([[[1,2,3], (42,None)], [4,5], [6], 7, (8,9,10)])
    [1, 2, 3, 42, None, 4, 5, 6, 7, 8, 9, 10]
    >>> flatten(["foo", "bar"])
    ['foo', 'bar']
    >>> flatten(["foo", ["baz", 42], "bar"])
    ['foo', 'baz', 42, 'bar']
    """
    return list(iflatten(x))


def iflatten(x):