Python 如何将函数的字符串输出转换为输入或可运行的shell命令？

例如，我使用这段代码为mask获取一个值

def get_rule(path, column_names):
    mask = ''
    for index, node in enumerate(path):
        #We check if we are not in the leaf
        if index!=len(path)-1:
            # Do we go under or over the threshold ?
            if (children_left[node] == path[index+1]):
                mask += "(df['{}']<= {}) \t ".format(column_names[feature[node]], threshold[node])
            else:
                mask += "(df['{}']> {}) \t ".format(column_names[feature[node]], threshold[node])
    # We insert the & at the right places
    mask = mask.replace("\t", "&", mask.count("\t") - 1)
    mask = mask.replace("\t", "")
    return mask

将给出错误：

KeyError: "(df['A']<= 0.12) & (df['B']> 0.07) & (df['C']<= 0.24) & (df['D']<= 4.0) & (df['A']> 0.92)"

您可能正在查找或函数。这些函数允许您以

str

的形式运行动态python代码

例如：

>>> df[output] 

exec("x = 1234")  # executes x = 1234 (set value of x to 1234)
eval("2 + 3 * 5")  # returns 17

因此，您可能希望这样使用它：

>>> output = get_rule(...)
>>> output

"(df['A']<= 0.12) & (df['B']> 0.07) & (df['C']<= 0.24) & (df['D']<= 4.0) & (df['A']> 0.92)"

eval(f"df[{output}]")  # Can't use exec() here because it doesn't return value

---

您需要字符串格式的结果吗？在执行过程中只计算结果，而不是在字符串上使用eval或exec，可能会很容易。

eval(f"df[{output}]")  # Can't use exec() here because it doesn't return value