def circle(x, y, radius, color=None, width=None):
    """Return a circle shape

    args:
        x, y (float): center coordinates
        radius (float): circle radius
        color (str): a plotly color string
        width (int): line width
    """
    data = {'type': 'circle', 'xref': 'x', 'yref': 'y', 'fillcolor':
        'rgba(50, 171, 96, 0.7)', 'x0': x - radius, 'y0': y - radius, 'x1':
        x + radius, 'y1': y + radius, 'line': {}}
    if color:
        data['line']['color'] = color
    if width:
        data['line']['width'] = width
    return data
