为什么我没有按时间序列为python数据框获取字符串正确的标签?

我想标记数据帧中的每个值,如果为零,则使用GND标记,而不是零,然后命名为Dry,但我只接收整个数据帧的GND标签。

result:

Timestamp   Dryer_power Label

2012-06-01 00:33:37 0.0 GND,
2012-06-01 00:33:38 0.0 GND,
2012-06-01 00:33:39 2.1906  GND,
2012-06-01 00:33:40 0.0 GND,
2012-06-01 00:33:41 0.0 GND,
2012-06-01 00:33:42 0.0 GND,
2012-06-01 00:33:43 0.0 GND,
2012-06-01 00:33:44 0.0 GND,
2012-06-01 00:33:45 0.0 GND,
2012-06-01 00:33:46 0.0 GND,
2012-06-01 00:33:47 2.1906  GND,
2012-06-01 00:33:48 0.0 GND,
2012-06-01 00:33:49 0.0 GND,

for i in df['Dryer_power'].iloc[:]:
    if(i == float(0)):
         df['Label'] = 'GND,'
    else:
         df['Label'] = 'Dry, '