如何解决Python脚本中的SettingWithCopyWarning警告？

我是Python新手，正在通过yfinance示例项目学习Python。运行以下脚本时出现SettingWithCopyWarning警告，查阅多篇相关文章后仍无法解决，恳请技术指导。

代码示例 #

# 设置感兴趣的时间范围
net_historical = net.history(start="2020-01-02", end="2022-10-21", interval="1d")

# 创建新的DataFrame signals，仅保留Date和Close列
#print(signals_df)
signals_df = net_historical.drop(columns=['Open', 'High', 'Low', 'Volume','Dividends', 'Stock Splits'])
signals_df = signals_df.copy()

# 设置短期和长期窗口
short_window = 50
long_window = 100

# 生成短期和长期移动平均线（分别为50日和100日）
signals_df['SMA50'] = signals_df['Close'].rolling(window=short_window).mean()
signals_df['SMA100'] = signals_df['Close'].rolling(window=long_window).mean()
signals_df['Signal'] = 0.0
signals_df['Symbol'] = line_strip

# 生成交易信号0或1：
# 当SMA50低于SMA100时为0，当SMA50高于（或交叉超过）SMA100时为1
signals_df['Signal'][short_window:] = np.where(
    signals_df['SMA50'][short_window:] > signals_df['SMA100'][short_window:], 1.0, 0.0
)

警告信息 #

See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy
  signals_df['Signal'][short_window:] = np.where(
/var/folders/xj/401632wd1qx7h6t0kqfjl98m0000gn/T/ipykernel_14492/214794330.py:59: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame

解决方法 #

这个警告是因为使用了链式索引（signals_df['Signal'][short_window:]）赋值，Pandas无法判断你操作的是原DataFrame还是它的副本，因此抛出警告。

直接改用Pandas官方推荐的.loc索引方式即可解决：

将原赋值代码替换为：

signals_df.loc[short_window:, 'Signal'] = np.where(
    signals_df.loc[short_window:, 'SMA50'] > signals_df.loc[short_window:, 'SMA100'], 1.0, 0.0
)

.loc通过行标签+列标签的组合明确指定操作区域，消除了副本/视图的歧义，自然就不会触发这个警告了。

内容的提问来源于stack exchange，提问作者chorink65