我正在制作一个带有覆盆子pi 3的7段显示器(4个显示器)记分板。我做了一个python程序,从数据库中读取2个数字并将它们存储在一个变量中,检查有多少位数(因为我只能发送一个数字到一个显示器)然后它将正确的信息发送到GPIO引脚。每个数字开启0.001s,因此0.004s全部通过4.然后循环总共200次重复,然后返回并检查数据库中是否有任何更改。
但是,当它从数据库重新读取时,所有显示都会关闭。我想知道是否有可能继续使用先前存储的变量循环(具有200次重复的循环)并且仅在数据库完成读取新信息之后用新的循环重新启动它。
#i have set up the database and all other important stuff outside this loop
while 1:
digitTipe = 0
digitTipe2 = 0
timer = 0 #counter for the GPIO loop
#it gets the info from db and then it lists the digits
cur.execute("SELECT gol_domaci FROM tekme ORDER BY id DESC LIMIT 0, 1")
db.commit()
home_team = cur.fetchall()
for q in home_team-:
digits= list(int(d) for d in str(q[0]))
#same but for the other team
cur.execute("SELECT gol_gosti FROM tekme ORDER BY id DESC LIMIT 0, 1")
db.commit()
guest_team = cur.fetchall()
for e in guest_team:
digit2 = list(int(d) for d in str(e[0]))
#here checks if both digits are the same (11, 22, 33...), is just one digit(3, 6, ...) or if is just a random number (12, 23, 45,...)
#based on these results the GPIO output knows how to properly send out voltage... i tried with other methods but this one works for me
if len(digit) < 2:
digitTipe = 1
else:
if digit[0] == digit[1]:
digitTipe = 2
if len(digit2) < 2:
digitTipe2 = 1
else:
if digit2[0] == digit2[1]:
digitTipe2 == 2
while timer < 200: #this is the loop that has code for GPIO pins
#("insert digit output code")
“滞后”并不坏,最多只有0.1秒,但这是显而易见的,令人讨厌,所以我的“同事”希望它固定下来。但如果可能的话,我不想制作两个单独的代码文件
我很抱歉编码的质量很差。这是我在python中的第一个“真正的”程序。我也很抱歉,如果我不够具体,因为它也恰好是我在stackoverflow上的第一个问题。提前致谢!
从我收集的,while timer < 200: …
循环激活显示。因此,当由于cur.execute(…)
等而未执行此循环时,显示器将被停用。
解决方案是使用异步编程。这是一个关于这个主题的好问题:asynchronous programming in python
这是一个复制并粘贴其中一个答案的例子(作者Jesse Dhillon):
from threading import Thread
def background_stuff():
while True:
print "I am doing some stuff"
t = Thread(target=background_stuff)
t.start()
# Continue doing some other stuff now
您可以创建两个类似于background_stuff
的函数,一个用于处理显示,另一个用于从数据库中获取信息。然后基于这两个函数实例化两个线程,并启动它们。所以:
# declare variables here
def handle_display():
while True:
# put here what is under the `while timer < 200: … ` loop
def fetch_from_db():
# every time timer runs out, fetch info from database
# and store in variables declared at line 1
t1 = Thread(target=handle_display)
t2 = Thread(target=fetch_from_db)
t1.start()
t2.start()