.. py:function:: pydu.list.uniq(seq, key=None)
Removes duplicate elements from a list while preserving the order of the rest.
The value of the optional ``key`` parameter should be a function that
takes a single argument and returns a key to test the uniqueness.
>>> from pydu.list import uniq
>>> uniq([1, 4, 0, 2, 0, 3])
[1, 4, 0, 2, 3]
.. py:function:: pydu.list.tolist(obj)
Convert given ``obj`` to list.
If ``obj`` is not a list, return ``[obj]``, else return ``obj`` itself.
>>> from pydu.list import tolist
>>> tolist('foo')
['foo']
.. py:function:: pydu.list.flatten(seq)
Generate each element of the given ``seq``. If the element is iterable and
is not string, it yields each sub-element of the element recursively.
>>> from pydu.list import flatten
>>> flatten([1, [2, [3, 4]]])
[1, 2, 3, 4]