TopolearnBuild tools, backups and security checks all decide what to do based on file metadata.
os.stat(path) returns a stat_result with the file's metadata:
st_sizesize in bytesst_mtimelast modification,st_atimelast access, as float seconds since the epoch (st_mtime_nsgives exact integer nanoseconds)st_modefile type and permission bits;st_uid,st_gidowner on Unixst_inoandst_devidentify the file; two paths with equal pairs are the same file
os.lstat (or follow_symlinks=False) describes a symlink itself rather than its target.
The stat module decodes st_mode: stat.S_ISDIR(mode), stat.S_ISREG(mode), and stat.filemode(mode) which renders it like ls -l, e.g. -rw-r--r--. The permission bits are mode & 0o777.
os.chmod(path, 0o600) sets permissions; write them in octal: owner, group, others, each a sum of read 4, write 2, execute 1. Add a bit with mode | stat.S_IXUSR. On Windows, chmod can only toggle the read-only flag.
New files get 0o666 (or 0o777 for directories) minus the process umask, typically 0o022, which is why files usually come out rw-r--r--.
os.access(path, os.W_OK) asks whether the real user could write, but like any check-then-act it can race; prefer attempting the operation and handling PermissionError.
Example
import os
import stat
import time
with open("secret.txt", "w") as f:
f.write("token=abc")
st = os.stat("secret.txt")
print(st.st_size) # 9
print(stat.S_ISREG(st.st_mode)) # True
print(abs(st.st_mtime - time.time()) < 5) # True
os.chmod("secret.txt", 0o600) # owner read/write only
mode = os.stat("secret.txt").st_mode
print(stat.filemode(mode)) # -rw-------
print(oct(mode & 0o777)) # 0o600
os.chmod("secret.txt", mode | stat.S_IXUSR)
print(stat.filemode(os.stat("secret.txt").st_mode)) # -rwx------Remember
os.statgives size, timestamps, mode, owner and identity of a file- Decode modes with the
statmodule; permissions arest_mode & 0o777 - Write chmod modes in octal; new files are 0o666 minus the umask
Watch out for
- Writing
os.chmod(p, 600)in decimal; that is0o1130, a nonsense mode. Use0o600.