尾部风险比率

def solve():
    import pandas as pd
    df = pd.read_csv(____)
    df['____'] = df['____'].pct_change()
    var = abs(df['____'].quantile(____))
    cvar = abs(df[df['____'] <= df['____'].quantile(____)]['____'].mean())
    ratio = cvar / var
    print(____)