sys — system parameters

import sys

Attributes

sys.argv — command-line arguments

A list[str] of arguments passed to the program. On this port, sys.argv starts out as [''] (no real argv is plumbed through the PMODE/W stub yet) — you can append to it from inside your script if you need to thread arguments through exec():

sys.argv = ['script.py', 'arg1', 'arg2']

sys.path — module search path

A list[str] of directories searched on import. Defaults to [''] (current directory only). Append to add more search roots:

sys.path.append('C:\\PYLIB')
import mylib       # found at C:\PYLIB\MYLIB.PY (DOS case-folds)

sys.modules — cache of imported modules

A dict of every module ever imported. Useful for unloading:

import sys, mymod
del sys.modules['mymod']        # next `import mymod` will re-execute

sys.stdin / sys.stdout / sys.stderr

The three standard streams as file-like objects. On DOS they map to handles 0/1/2 (the DOS console by default, or whatever CTTY redirected them to).

sys.stdout.write('no newline')
sys.stderr.write('warning!\n')
line = sys.stdin.readline()

sys.platform — 'fdmp'

Identifies this port. Use it to write code that’s only run on FreeDOS:

if sys.platform == 'fdmp':
    # DOS-specific path
    ...

sys.implementation — version + capability info

A named tuple:

>>> sys.implementation
(name='micropython', version=(1, 26, 0), _machine='uc386-dos with i386', _mpy=4358)

sys.version — MicroPython version string

>>> sys.version
'3.4.0; MicroPython v1.26.0'

sys.byteorder — 'little'

i386 is little-endian.

sys.maxsize — largest small-int

Used in places where you’d want a sentinel like “infinity in integer terms”. On i386 PMODE/W: 2**30 - 1 (small ints are 30-bit; bigger uses heap allocation).

Functions

sys.exit(code=0)

Raises SystemExit(code), which (if uncaught) terminates the program. code should be a small integer; it’s returned to DOS via INT 21h AH=0x4C and surfaces as %ERRORLEVEL%.

import sys
sys.exit(0)                # success
sys.exit(1)                # error

sys.print_exception(exc, file=sys.stdout)

Prints the traceback for an exception. Useful in except:

try:
    something()
except Exception as e:
    sys.print_exception(e)

sys.exc_info()

Returns (type, value, traceback) for the currently-handled exception (or (None, None, None) if none).

sys.atexit(fn)

Registers a function to be called on program exit. Mainly used by libraries that need to flush state.

Attributes (introspection)

sys.tracebacklimit

Cap traceback depth. Set to a small number on tiny screens:

sys.tracebacklimit = 3

sys.maxsize, sys.maxlong — see “Attributes” above

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Credit: adapted from MicroPython sys docs (MIT, © 2014-2024 Damien P. George and contributors).