用python写文件真的不要太简单，也是自己工作中常用的

with open('1.txt', 'w') as f:
	f.write('xxxx')

但这种方式通常在文件写完，即隐式调用了close()方法之后才会生成文件
我当前需要每写完一行数据，就在文件中立刻看到，即写入内容实时落盘，该怎么办？

方法一

查了下open()方法，发现通过参数(buffering)可以实现:

def open(file, mode='r', buffering=None, encoding=None, errors=None, newline=None, closefd=True): # known special case of open
	“”“
	...
	buffering is an optional integer used to set the buffering policy.
    Pass 0 to switch buffering off (only allowed in binary mode), 1 to select
    line buffering (only usable in text mode), and an integer > 1 to indicate
    the size of a fixed-size chunk buffer.  When no buffering argument is
    given, the default buffering policy works as follows:
	...
	”“”

当buffering=0时关闭缓冲区，写入内容实时落盘，赶快验证一下：

import time
with open("1.txt", "w", buffering=0) as f:
    for x in range(10):
        time.sleep(1)
        f.write("qwert\n")

运行, 结果…

ValueError: can't have unbuffered text I/O

text不让关闭缓冲写，试试二进制文件(其实函数说明中已经说明了，自己没仔细看而已：only allowed in binary mode)：

import time
with open("1.txt", "wb", buffering=0) as f:
    for x in range(10):
        time.sleep(1)
        f.write(b"qwert\n")

再次运行，成功，内容实时落地

[root@centos78 wangwei]# tail -f 1.txt
qwert
qwert
qwert
qwert
qwert
qwert

方法二

还可以通过flush()方法自己控制将buffer内容落盘的时机

import time
with open("1.txt", "w") as f:
    for x in range(10):
        time.sleep(1)
        f.write("qwert\n")
        f.flush()

这样同样能达到写入内容实时落盘的效果