为什么python在time.sleep()之后不打印? [英] Why python don't print after a time.sleep()?

问题描述

我用 python 编程将近 2 年了，我在看一些旧代码时发现了一个非常奇怪的事情.

I'm programming in python for almost 2 years and I found a really weird thing when watching some old code.

import random, sys, time

try:
    while True:
        print(' ', str(random.randint(100,999)), end='')
        time.sleep(0.01)
except:
    sys.exit()

按照这段代码的语法，我的程序应该永远打印一个空格和一个从 100 到 999 的随机数，但这并没有发生.

Following the syntax of this code my program should print a space and a random number from 100 to 999 forever, but this isn't happening.

当我运行这段代码时，在我按下 CTRL-C 之前，屏幕上什么都没有出现，即使删除了 try 语句也不会改变任何东西.

When I run this code nothing appear on the screen until I press CTRL-C, even removing the try statement din't change anything.

我尝试更改控制台(Windows 终端、powershell 和 CMD)，但没有任何反应.

I tried changing console (Windows terminal, powershell and CMD) but nothing happened.

有人可以帮我解决这个问题吗?谢谢

Can please someone help me out with this? Thanks

推荐答案

Python 将打印输出保存在缓冲区中，并在实际显示之前等待行尾.要在 Python 3 中强制显示，可以添加关键字 flush=True.

Python keeps your print outputs in a buffer and waits for the end of the line before actually displaying it. To force the display in Python 3, you can add the keyword flush=True.

import random, sys, time

try:
    while True:
        print(' ', str(random.randint(100,999)), end='', flush=True)
        time.sleep(0.01)
except:
    sys.exit()

或者，您可以:

• 在打印后调用 sys.stdout.flush()(Python 2 兼容)；
• 在执行脚本时使用 -u 标志 (python -u script.py);
• 将环境变量 PYTHONUNBUFFERED 设置为 TRUE.

• call sys.stdout.flush() after the print (Python 2-compatible);
• use the -u flag when executing the script (python -u script.py);
• set the environment variable PYTHONUNBUFFERED to TRUE.

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