用pyecharts写一个3层的桑基图，第一层节点为A1、A2和A3，大小分别为10、7和5，第二层为B1和B2，大小分别为9和3，第三层为C1和C2，大小分别为4和6。要求A1于B1连接，A2同时与B1和B2连接，B1和B2同时与C1连接，A3又和C2连接。

好的，以下是用pyecharts实现的代码：

from pyecharts import options as opts
from pyecharts.charts import Sankey

nodes = [
    {"name": "A1"},
    {"name": "A2"},
    {"name": "A3"},
    {"name": "B1"},
    {"name": "B2"},
    {"name": "C1"},
    {"name": "C2"},
]

links = [
    {"source": "A1", "target": "B1", "value": 10},
    {"source": "A2", "target": "B1", "value": 7},
    {"source": "A2", "target": "B2", "value": 7},
    {"source": "A3", "target": "C2", "value": 5},
    {"source": "B1", "target": "C1", "value": 9},
    {"source": "B2", "target": "C1", "value": 3},
    {"source": "B1", "target": "C2", "value": 1},
    {"source": "B2", "target": "C2", "value": 5},
]

sankey = (
    Sankey()
    .add(
        "sankey",
        nodes=nodes,
        links=links,
        itemstyle_opts=opts.ItemStyleOpts(border_width=1, border_color="#aaa"),
        linestyle_opt=opts.LineStyleOpts(opacity=0.2, curve=0.5, color="source"),
        label_opts=opts.LabelOpts(position="right"),
    )
    .set_global_opts(
        title_opts=opts.TitleOpts(title="三层桑基图"),
        tooltip_opts=opts.TooltipOpts(trigger_on="mousemove"),
    )
    .render("sankey.html")
)

生成的图如下：