Question

根据文档，如果我使用open（“file”，“a”）并写入文件，则会附加新数据，但在下面的示例中，第二个命令只是覆盖文件。我不明白为什么。

import subprocess

startupinfo = subprocess.STARTUPINFO()
subprocess.STARTF_USESHOWWINDOW = 1
startupinfo.dwFlags = subprocess.STARTF_USESHOWWINDOW

with open(r"c:\folder\test.txt","a") as log:
    Process = subprocess.Popen(['dir'],
                               stdout = log, stderr = log,
                               startupinfo = startupinfo,
                               shell=True)

with open(r"c:\folder\test.txt","a") as log:
    Process = subprocess.Popen(['dir'],
                               stdout = log, stderr = log,
                               startupinfo = startupinfo,
                               shell=True)

我已经尝试了模式“a + b”，但我得到了相同的最终结果。

Answer 1

在subprocess范围内，文件位置不会增加。 log.tell()在第二个0语句中返回with。您可以将log的位置加到文件末尾。对于第一个wait()，Process似乎很好。以下是我的工作：

import subprocess
from os import linesep, stat 

with open(r"test.txt","a") as log:
    Process = subprocess.Popen(['dir'],
                               stdout = log, stderr = log,
                               shell=True)
    Process.wait()

with open(r"test.txt","a") as log:
# this prints 0
    print log.tell()
# get the length of the file log
    pos = stat(r"test.txt").st_size
    print pos
# go to the end of log
    log.seek(pos)
    Process = subprocess.Popen(['dir'],
                               stdout = log, stderr = log,
                               shell=True)

Python open + append没有按预期工作

1 个答案: