如何每隔n秒执行某件事，同时使用Python做其他事情

Question

I'm doing this on a raspberry pi. I'm very new to python I recently moved from arduino to raspberry for this project.

I want to send temp to db every 5 seconds but I want to update the graph every 1 minute. However, the graph doesn't update it gets stuck in writeLog. I wrote print "loop" after s.run but it doesn't show. Next I wrote print "here" after s.enter() in writeLog and it shows.

Also I couldn't place plotNow inside sched (Error not in main loop). I tried threading but I couldn't get 60sec for the loop.

Here's my current code:

from matplotlib import pyplot as plt
from datetime import datetime

import MySQLdb
import sched, time

s = sched.scheduler(time.time, time.sleep)

db = MySQLdb.connect(host="localhost", user="root", passwd="", db="log")
cur = db.cursor()

cnt = 0    

tempC = []

plt.ion()
plt.figure(figsize=(10,5))


def writeLog(sc):
    print "Insert to DB"
    try:
        st = "%.2f" % thermoTempC        
        cur.execute("""INSERT INTO history (Datetime, Temp_Degrees, Remarks) VALUES (%s, %s, %s)""", (datetime.now().strftime('%Y-%m-%d %H:%M:%S'), st, 'OK'))
        db.commit()
    except:
        db.rollback()
    s.enter(5,1,writeLog,(sc,))    


def plotNow():
    plt.clf()
    plt.grid(True)        
    plt.title('Current Temp = {:.2f}$^\circ$C'.format(thermoTempC), fontsize=15)   
    plt.ylabel('Temperature(C)')
    plt.xlabel('Time(min)')
    plt.xlim(0,120)
    plt.ylim(0,90)    
    plt.plot(tempC, 'r.-', label='Actual', color='red')
    plt.legend(loc='upper right')   
    plt.show(block=False)


while True:            
    thermoTempC = "32.00"

    tempC.append(thermoTempC)    
    plotNow()
    plt.pause(.1)
    cnt = cnt+1

    if(cnt>120):
        tempC.pop(0)    

    s.enter(5,1,writeLog,(s,))
    s.run()

Answer 1

I couldn't find the duplicate-ish question I was looking for, so here is my answer.

You can put each of your processes in a thread, using the threading module.

Let's say you have a send_temp_db and a update_graph functions, which respectively perform the elementary action of sending the temperature once, and updating the graph once.

You'll need to define two functions that will run continuously:

def send_temp_loop():
    while True:
        send_temp_db(...)
        time.sleep(5)   # wait for 5s

def update_graph_loop():
    while True:
        update_graph(...)
        time.sleep(60)  # wait for 60s

Then, create one thread for both actions, and run the two threads.

thread_temp = threading.Thread(target=send_temp_loop)
thread_graph = threading.Thread(target=update_graph_loop)

thread_temp.start()
thread_graph.start()

thread_temp.join()

Don't forget to join one of your threads. If you don't, the program will exit right after the two threads start.