我在樹莓派上有一些 python 代碼，我想運(yùn)行并繼續(xù)循環(huán)，直到按下按鈕。button.wait_for_press() 不合適，因?yàn)樗鼤?huì)暫停程序直到它運(yùn)行，但我已經(jīng)試過了，看看硬件是否工作正常。def shutterPressed(): global shutterHasBeenPressed shutterHasBeenPressed = Truedef main(): """ Main program loop """ #start camera preview camera.start_preview(resolution=(SCREEN_W, SCREEN_H)) #Display Intro screens intro_image_1 = REAL_PATH + '/assets/intro_1.png' intro_image_2 = REAL_PATH + '/assets/intro_2.png' overlay_1 = overlay_image(intro_image_1, 0, 3) overlay_2 = overlay_image(intro_image_2, 0, 4) #Wait for button press i = 0 blink_speed = 10 button.when_pressed = shutterPressed while True: global shutterHasBeenPressed shutterHasBeenPressed = False #Stay in loop until button is pressed if shutterHasBeenPressed is False: i += 1 if i == blink_speed: overlay_2.alpha = 255 elif i == (2 * blink_speed): overlay_2.alpha = 0 i = 0 #Restart while loop sleep(0.1) continue #button has been pressed! print("Button Pressed!")當(dāng)我運(yùn)行此代碼時(shí)，根本沒有注冊按鈕按下。我做錯(cuò)了什么？編輯：所以我在shutterPressed() 函數(shù)中添加了一個(gè)打印語句，并確認(rèn)它在按下按鈕時(shí)正在運(yùn)行。In 還添加了一個(gè)語句，用于在 if 語句之前打印shutterHasBeenPressed 的值。這從未改變過虛假。但是，如果我刪除了在循環(huán)開始時(shí)將變量更改為 false 的行，那么代碼就起作用了，所以這顯然與運(yùn)行各種位有關(guān)。也許在shutterPressed() 函數(shù)運(yùn)行后while 循環(huán)又開始了？無論哪種方式，我都通過將變量的重新分配移到 if 語句之后來修復(fù)它。
1 回答
幕布斯7119047
TA貢獻(xiàn)1794條經(jīng)驗(yàn) 獲得超8個(gè)贊
歡迎來到并發(fā)世界（有點(diǎn)）！
試想一下，你的程序運(yùn)行：根據(jù)執(zhí)行流程，他們定義的指令正在執(zhí)行一個(gè)接一個(gè)的在它們的排列順序后，與例外的shutterPressed這是異步執(zhí)行的（可能）。
因此，假設(shè)我們進(jìn)入循環(huán)并在第一行<here>：
while True:
global shutterHasBeenPressed
shutterHasBeenPressed = False # <here>
#Stay in loop until button is pressed
if shutterHasBeenPressed is False:
i += 1
if i == blink_speed:
overlay_2.alpha = 255
elif i == (2 * blink_speed):
overlay_2.alpha = 0
i = 0
#Restart while loop
sleep(0.1)
continue
#button has been pressed!
print("Button Pressed!")
現(xiàn)在，shutterHasBeenPressed已設(shè)置為False并且驗(yàn)證了隨后的條件，以便我們輸入if.
程序一直運(yùn)行，直到意外地按下按鈕。說，它達(dá)到了<here>：
while True:
global shutterHasBeenPressed
shutterHasBeenPressed = False
#Stay in loop until button is pressed
if shutterHasBeenPressed is False:
i += 1
if i == blink_speed:
overlay_2.alpha = 255 # <here>
elif i == (2 * blink_speed):
overlay_2.alpha = 0
i = 0
#Restart while loop
sleep(0.1)
continue
#button has been pressed!
print("Button Pressed!")
此時(shí)，shutterPressed運(yùn)行，設(shè)置shutterHasBeenPressed為True。然后，回到我們的循環(huán)，迭代結(jié)束，我們continue在循環(huán)的開始......那里有什么？！
shutterHasBeenPressed = False
按下按鈕完全沒有引起注意！
我相信這可以回答您的問題，詢問您做錯(cuò)了什么。
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