如何刷新打印功能的输出？

Question

如何强制Python的打印函数输出到屏幕？

_{这不是Disable output buffering的副本-链接的问题正在尝试无缓冲输出，而这更为一般。这个问题的主要答案对这个问题来说太强大了或者太复杂了（对这个问题来说他们不是很好的答案），这个问题可以在谷歌上被一个相对的新手找到。}

Answer 1

运行python -h，我看到一个命令行选项：

-u : unbuffered binary stdout and stderr; also PYTHONUNBUFFERED=x see man page for details on internal buffering relating to '-u'

这是relevant doc。

Answer 2

在Python 3上，^{}可以采用可选的flush参数

print("Hello world!", flush=True)

在Python 2上，您必须执行以下操作

import sys
sys.stdout.flush()

在调用print之后。默认情况下，^{}打印到^{}（有关file objects的详细信息，请参阅文档）。

Answer 3

自Python 3.3以来，您可以强制普通的print()函数刷新，而无需使用sys.stdout.flush()；只需将“flush”关键字参数设置为true。来自the documentation：

print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)

Print objects to the stream file, separated by sep and followed by end. sep, end and file, if present, must be given as keyword arguments.

All non-keyword arguments are converted to strings like str() does and written to the stream, separated by sep and followed by end. Both sep and end must be strings; they can also be None, which means to use the default values. If no objects are given, print() will just write end.

The file argument must be an object with a write(string) method; if it is not present or None, sys.stdout will be used. Whether output is buffered is usually determined by file, but if the flush keyword argument is true, the stream is forcibly flushed.