human
Here's a good function header given the following:
I wrote the below code

    data = {'a': [1, 2], 'b': [8, 9], 'x': 'xyz'}
    @_preprocess_data(label_namer='y')
    def func_replace_all(ax, x, y, ls='x', label=None, w='NOT'):
        return ('x:    %s,    y:    %s,    ls:    %s,    w:    %s,    label:    %s' % (list(x), list(y), ls, w, label))
    assert (func_replace_all(None, 'a', 'b', w='x', data=data) == 'x:    [1,    2],    y:    [8,    9],    ls:    x,    w:    xyz,    label:    b')
    assert (func_replace_all(None, x='a', y='b', w='x', data=data) == 'x:    [1,    2],    y:    [8,    9],    ls:    x,    w:    xyz,    label:    b')
    assert (func_replace_all(None, 'a', 'b', w='x', label='', data=data) == 'x:    [1,    2],    y:    [8,    9],    ls:    x,    w:    xyz,    label:    ')
    assert (func_replace_all(None, 'a', 'b', w='x', label='text', data=data) == 'x:    [1,    2],    y:    [8,    9],    ls:    x,    w:    xyz,    label:    text')
    assert (func_replace_all(None, x='a', y='b', w='x', label='', data=data) == 'x:    [1,    2],    y:    [8,    9],    ls:    x,    w:    xyz,    label:    ')
    assert (func_replace_all(None, x='a', y='b', w='x', label='text', data=data) == 'x:    [1,    2],    y:    [8,    9],    ls:    x,    w:    xyz,    label:    text')
    @_preprocess_data(label_namer='y')
    def func_varags_replace_all(ax, *args, **kwargs):
        all_args = [None, None, 'x', None, 'xyz']
        for (i, v) in enumerate(args):
            all_args[i] = v
        for (i, k) in enumerate(['x', 'y', 'ls', 'label', 'w']):
            if (k in kwargs):
                all_args[i] = kwargs[k]
        (x, y, ls, label, w) = all_args
        return ('x:    %s,    y:    %s,    ls:    %s,    w:    %s,    label:    %s' % (list(x), list(y), ls, w, label))
    assert (func_varags_replace_all(None, x='a', y='b', w='x', data=data) == 'x:    [1,    2],    y:    [8,    9],    ls:    x,    w:    xyz,    label:    b')
    assert (func_varags_replace_all(None, 'a', 'b', w='x', label='', data=data) == 'x:    [1,    2],    y:    [8,    9],    ls:    x,    w:    xyz,   ...

What's a good function header?
assistant
#Here's a good function header.

def test_function_call_replace_all():