如何获取Python中的默认文件权限？

Question

我正在编写一个 Python 脚本，其中我将输出写入临时文件，然后在完成并关闭后将该文件移动到其最终目的地。脚本完成后，我希望输出文件具有与通过 open(filename,"w") 正常创建的权限相同的权限。事实上，该文件将具有临时文件模块对临时文件使用的限制性权限集。

有没有办法让我弄清楚如果我就地创建输出文件，它的“默认”文件权限是什么，以便我可以在移动临时文件之前将它们应用到临时文件？

Answer 1

作为记录，我遇到了类似的问题，这是我使用的代码：

import os
from tempfile import NamedTemporaryFile

def UmaskNamedTemporaryFile(*args, **kargs):
    fdesc = NamedTemporaryFile(*args, **kargs)
    # we need to set umask to get its current value. As noted
    # by Florian Brucker (comment), this is a potential security
    # issue, as it affects all the threads. Considering that it is
    # less a problem to create a file with permissions 000 than 666,
    # we use 666 as the umask temporary value.
    umask = os.umask(0o666)
    os.umask(umask)
    os.chmod(fdesc.name, 0o666 & ~umask)
    return fdesc

Answer 2

os< 中有一个函数 umask /code> 模块。您无法获取当前的 umask 本身，您必须设置它并且该函数返回之前的设置。

umask 是从父进程继承的。它描述了创建文件或目录时不要设置的位。

Answer 3

这种方式虽然缓慢但安全，并且适用于任何具有“umask”shell 命令的系统：

def current_umask() -> int:
  """Makes a best attempt to determine the current umask value of the calling process in a safe way.

  Unfortunately, os.umask() is not threadsafe and poses a security risk, since there is no way to read
  the current umask without temporarily setting it to a new value, then restoring it, which will affect
  permissions on files created by other threads in this process during the time the umask is changed.

  On recent linux kernels (>= 4.1), the current umask can be read from /proc/self/status.

  On older systems, the safest way is to spawn a shell and execute the 'umask' command. The shell will
  inherit the current process's umask, and will use the unsafe call, but it does so in a separate,
  single-threaded process, which makes it safe.

  Returns:
      int: The current process's umask value
  """
  mask: Optional[int] = None
  try:
    with open('/proc/self/status') as fd:
      for line in fd:
        if line.startswith('Umask:'):
          mask = int(line[6:].strip(), 8)
          break
  except FileNotFoundError:
    pass
  except ValueError:
    pass
  if mask is None:
    import subprocess
    mask = int(subprocess.check_output('umask', shell=True).decode('utf-8').strip(), 8)
  return mask

Answer 4

import os

def current_umask() -> int:
    tmp = os.umask(0o022)
    os.umask(tmp)
    return tmp

这个函数在一些python包中实现，例如 点 和 安装工具。