我无法让重启按钮在我的秒表上工作。在 iPhone 上使用 Pythonista

Question

import ui
from time import *
start = int(time())
def stop_time(sender):
    finish = int(time())
    total_time = int(finish - start)
    button1 = str("Your time is %i seconds." % (total_time))
    sender.title = None
    sender.title = str(button1)

如何允许重启按钮更改启动变量？

def restart_time(sender):
    start = int(time())
    button2 = str("Stopwatch restarted.")
    sender.title = None
    sender.title = str(button2)
ui.load_view('stop_time').present('sheet')

Answer 1

默认情况下，当您第一次在函数中分配一个标识符时，它会创建一个局部变量，即使存在同名的全局变量也是如此。试试这个：

def restart_time(sender):
    global start
    start = int(time())
    button2 = str("Stopwatch restarted.")
    sender.title = None
    sender.title = str(button2)

来自the relevant entry in the Python FAQ：

In Python, variables that are only referenced inside a function are implicitly global. If a variable is assigned a new value anywhere within the function’s body, it’s assumed to be a local. If a variable is ever assigned a new value inside the function, the variable is implicitly local, and you need to explicitly declare it as ‘global’.