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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fill_between( x=None, ylow=None, yhigh=None, label=None, color=None, width=None, dash=None, opacity=None, mode='lines+markers', **kargs ):
 """Fill between `ylow` and `yhigh`. Parameters x : array-like, optional ylow : TODO, optional yhigh : TODO, optional Returns ------- Chart """

    plot = line(
        x=x,
        y=ylow,
        label=label,
        color=color,
        width=width,
        dash=dash,
        opacity=opacity,
        mode=mode,
        fill=None,
        **kargs
    )
    plot += line(
        x=x,
        y=yhigh,
        label=label,
        color=color,
        width=width,
        dash=dash,
        opacity=opacity,
        mode=mode,
        fill='tonexty',
        **kargs
    )
    return plot