请用python编码码：读入如下格式的asst.csv文件 交易日 策略 品种 单位净值 20230130 BDE000-15 SH512000 0.991367 20230130 BDE000-20 SH512000 1 20230130 BDE000-30 SH512000 1 20230130 BDE030-15 SH515030 1 20230130 BDE030-20 SH515030 1 20230130 BDE030-30 SH515030 1 20230130 BDE030-5 SH515030 0.983256 20230130 BDE170-15 SH512170 1 20230130 BDE170-20 SH512170 1 20230130 BDE170-30 SH512170 1 20230130 BDE170-5 SH512170 1 20230130 BDE290-10 SH512290 1 20230130 BDE290-15 SH512290 1 20230130 BDE290-20 SH512290 0.986876 20230130 BDE290-30 SH512290 1 20230130 BDE290-5 SH512290 1 20230130 BDE660-10 SH512660 1.007269 20230130 BDE660-15 SH512660 1.007269 20230130 BDE660-5 SH512660 1.022703 20230130 BDE690-10 SH512690 1 20230130 BDE690-15 SH512690 0.997257 20230130 BDE690-20 SH512690 0.997257 20230130 BDE690-30 SH512690 1 20230130 BDE690-5 SH512690 1 20230130 BDE790-15 SH515790 1.004192 20230130 BDE790-20 SH515790 1.005566 20230130 BDE790-30 SH515790 1.003483 20230130 BDE790-5 SH515790 1.007581 20230130 BDE880-20 SH512880 1 20230130 BDE915-15 SZ159915 1.007231 20230130 BDE915-20 SZ159915 1.007231 20230130 BDE915-5 SZ159915 1 20230130 BDE949-15 SZ159949 0.983253 20230130 BDE949-20 SZ159949 1.02574 20230130 BDE949-30 SZ159949 1.013246 20230130 BDE949-5 SZ159949 1 20230130 BDE995-20 SZ159995 1 20230130 BDE995-30 SZ159995 1 20230130 BDE995-5 SZ159995 1 20230130 BDG688005 SH688005 1.01585， 然后格局数据绘制交易日-单位净值曲线，可以交互选择单个，多个或全部策略

import pandas as pd
import matplotlib.pyplot as plt

# 读入asst.csv文件
data = pd.read_csv("asst.csv", sep=" ")
# 将交易日转换为日期格式
data['交易日'] = pd.to_datetime(data['交易日'], format='%Y%m%d')
# 设定index为交易日
data.set_index('交易日', inplace=True)

# 绘制交易日-单位净值曲线
fig, ax = plt.subplots()

# 定义选择策略的下拉菜单
strategy_options = ['全部'] + list(data['策略品种'].unique())
initial_strategy = '全部'
select_strategy = plt.widgets.Dropdown(options=strategy_options, value=initial_strategy, description='策略品种')

# 单个或多个策略选择函数
def select_strategy_handler(change):
if change.new != '全部':
selected_data = data[data['策略品种']==change.new]
ax.clear()
ax.plot(selected_data.index, selected_data['单位净值'])
ax.set(title=change.new)
else:
ax.clear()
for strategy in strategy_options[1:]:
selected_data = data[data['策略品种']==strategy]
ax.plot(selected_data.index, selected_data['单位净值'])
ax.set(title='全部策略')

select_strategy.observe(select_strategy_handler, names='value')
plt.show()