我正在编写一个 Python 脚本，在该脚本中我将输出写入一个临时文件，然后在完成并关闭该文件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。实际上，该文件将具有 tempfile 模块用于临时文件的一组限制性权限。
如果我在适当位置创建输出文件，我有没有办法弄清楚输出文件的“默认”文件权限是什么，以便在移动临时文件之前将它们应用到临时文件？
【问题讨论】：
标签： python file-permissions temporary-files
记录一下，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
【讨论】：
os.umask(0) 是一个潜在的安全问题，请参阅bugs.python.org/issue21082。
有一个函数umask in the os 模块。您无法获取当前的 umask 本身，您必须设置它并且函数返回之前的设置。
umask 继承自父进程。它描述了在创建文件或目录时不设置哪些位。
【讨论】：
os.umask 一次，保存返回值，然后使用该值再次调用它以恢复它，然后从该掩码中获取适当的权限？
tempfile吗？
这种方式速度慢但安全，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
【讨论】：
import os
def current_umask() -> int:
tmp = os.umask(0o022)
os.umask(tmp)
return tmp
此功能在一些 python 包中实现，例如pip 和 setuptools。
【讨论】：