Python循环一整天，当当前时间等于给定时间时，做些什么

Question

我有一个Pandas数据帧df，它有三列（time，from和to）。我想执行一个函数，它将执行for循环df['time']。当当前时间等于df['time']中的时间时，调用另一个函数，如print something。每行只执行一次。在实际数据中，脚本将在云中24小时执行。你知道吗

import pandas as pd
df=pd.DataFrame({'time':['08:35','09:35','09:45','10:10'],
                 'from':['SHH','SZH','WXH','ZJH'],
                 'to':['NJH','NJH','NJH','NJH']})
df

    from    time    to
0   SHH     08:35   NJH
1   SZH     09:35   NJH
2   WXH     09:45   NJH
3   ZJH     10:10   NJH

例如，当前时间为08:35时，打印Time is reached, train from SHH to NJH；当前时间为09:35时，打印Time is reached, train from SZH to NJH。我不知道如何修改下面的代码来满足我的要求 工作。我需要帮助。你知道吗

import datetime
import time

def ex(a,b):
    print("Time is reached. train from {} to {}".format(a, b))

time_ls = list(df['time'])
from_ls = list(df['from'])
to_ls = list(df['to'])

def run():
    for i in range(len(df['time'])):
        while time.strftime("%H:%M", time.localtime()) == df['time'][i]:
            time_ls.remove(df['time'][i])
            yield ex(from_ls[i],to_ls[i])

Answer 1

如果要从满足特定条件的pandas.DataFrame中提取行，则需要对DataFrame进行切片，而不是手动迭代其所有行并自行检查该条件。这种方法的pandas实现比任何手动尝试都要快。你知道吗

一旦您得到了只包含与当前时间（小时和分钟）匹配的行的数据帧，您就可以迭代较小的DataFrame并打印它的每一行的结果（因为您知道它只包含那些匹配的行）。你知道吗

请参见以下示例：

from datetime import datetime as dt
import pandas as pd

if __name__ == '__main__':
    df = pd.DataFrame({
        'time': ['08:35','09:35','09:45','10:10'],
        'from': ['SHH','SZH','WXH','ZJH'],
        'to':   ['NJH','NJH','NJH','NJH']})

    ct = dt.strftime(dt.now(), '%H:%M') # Get current hours and minutes
    dn = df.loc[df['time'] == ct] # Slice DataFrame based on 'time' column

    for row in dn.iterrows():
        # Iterate over all rows that meet the condition and print it
        print('{time:s}   train from {from:s} to {to:s}.'.format(**dict(row[1])))

它产生（对于本例，如果ct字符串的小时和分钟与08:35匹配）：

08:35   train from SHH to NJH.