os — filesystem and environment

import os

DOS-specific notes are flagged with ⚠️.

Filesystem

os.listdir(path='.')

List entries in a directory. Returns a list[str].

>>> os.listdir()
['MP.EXE', 'NE2000.COM', 'HELLO.PY', 'AUTOEXEC.BAT', '.', '..']
>>> os.listdir('C:\\')
['DOS', 'AUTOEXEC.BAT', 'CONFIG.SYS', ...]

⚠️ DOS includes the . and .. entries in the directory listing. Strip them yourself if you don’t want them:

files = [f for f in os.listdir() if f not in ('.', '..')]

os.stat(path)

Returns a tuple of file info: (mode, ino, dev, nlink, uid, gid, size, atime, mtime, ctime). Most fields are DOS-meaningless (ino/uid/gid are 0); size and mtime are real.

>>> os.stat('HELLO.PY')
(32768, 0, 0, 0, 0, 0, 67, 0, 1747630800, 0)
#   ↑                       ↑
#   mode (S_IFREG)          size in bytes

os.remove(path) / os.unlink(path)

Delete a file.

os.rename(old, new)

Rename / move a file. On DOS this is INT 21h AH=0x56 and works within a single drive only.

os.mkdir(path) / os.rmdir(path)

Create / remove a directory. Standard DOS rules: empty for rmdir.

os.chdir(path) / os.getcwd()

Change / get the current working directory. The DOS current directory is per-drive, so getcwd() returns something like 'A:\\DOS'.

os.path.* — path helpers

A minimal subset:

>>> os.path.join('C:\\DOS', 'AUTOEXEC.BAT')
'C:\\DOS\\AUTOEXEC.BAT'
>>> os.path.basename(_)
'AUTOEXEC.BAT'

Environment

os.getenv(name, default=None)

Read a DOS environment variable (set with SET name=value in COMMAND.COM):

>>> os.getenv('PATH')
'C:\\DOS;C:\\WINDOWS;...'
>>> os.getenv('NONESUCH', '<unset>')
'<unset>'

os.environ — full env as a dict

⚠️ Mutating os.environ does NOT propagate to the parent shell when MP exits. DOS doesn’t have a putenv syscall that affects the parent; the change is purely in-process.

Misc

os.urandom(n)

Returns n bytes of random data. On this port, seeded from the BIOS tick counter at startup; sufficient for non-crypto uses. Do not use as a CSPRNG.

os.uname()

Returns a (sysname, nodename, release, version, machine) named tuple:

>>> os.uname()
(sysname='fdmp', nodename='fdmp', release='1.26.0',
 version='MicroPython v1.26.0 on 2026-05-01', machine='uc386-dos with i386')

File-descriptor I/O

The lower-level file API (os.open, os.read, os.write, os.close, os.lseek) is available — open() actually delegates to it. Use it when you need INT 21h-flavoured semantics directly.

fd = os.open('FILE.TXT', os.O_RDONLY)
data = os.read(fd, 1024)
os.close(fd)

Open flags: os.O_RDONLY, os.O_WRONLY, os.O_RDWR.

DOS-specific helpers

For raw INT 21h dispatch, see dosint21. For direct memory access, see machine.

Credit: surface adapted from MicroPython os docs (MIT, © 2014-2024 Damien P. George and contributors). DOS notes are this port’s.