sys – system specific functions


Though this MicroPython-based library may be available for use in some builds of CircuitPython, it is unsupported and its functionality may change in the future, perhaps significantly. As CircuitPython continues to develop, it may be changed to comply more closely with the corresponding standard Python library. You will likely need to change your code later if you rely on any non-standard functionality it currently provides.

This module implements a subset of the corresponding CPython module, as described below. For more information, refer to the original CPython documentation: sys.



Terminate current program with a given exit code. Underlyingly, this function raise as SystemExit exception. If an argument is given, its value given as an argument to SystemExit.

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

Print exception with a traceback to a file-like object file (or sys.stdout by default).

Difference to CPython

This is simplified version of a function which appears in the traceback module in CPython. Unlike traceback.print_exception(), this function takes just exception value instead of exception type, exception value, and traceback object; file argument should be positional; further arguments are not supported.



A mutable list of arguments the current program was started with.


The byte order of the system ("little" or "big").


Object with information about the current Python implementation. For CircuitPython, it has following attributes:

  • name - string “circuitpython”
  • version - tuple (major, minor, micro), e.g. (1, 7, 0)

This object is the recommended way to distinguish CircuitPython from other Python implementations (note that it still may not exist in the very minimal ports).

Difference to CPython

CPython mandates more attributes for this object, but the actual useful bare minimum is implemented in CircuitPython.


Maximum value which a native integer type can hold on the current platform, or maximum value representable by CircuitPython integer type, if it’s smaller than platform max value (that is the case for CircuitPython ports without long int support).

This attribute is useful for detecting “bitness” of a platform (32-bit vs 64-bit, etc.). It’s recommended to not compare this attribute to some value directly, but instead count number of bits in it:

bits = 0
v = sys.maxsize
while v:
    bits += 1
    v >>= 1
if bits > 32:
    # 64-bit (or more) platform
    # 32-bit (or less) platform
    # Note that on 32-bit platform, value of bits may be less than 32
    # (e.g. 31) due to peculiarities described above, so use "> 16",
    # "> 32", "> 64" style of comparisons.

Dictionary of loaded modules. On some ports, it may not include builtin modules.


A mutable list of directories to search for imported modules.


The platform that CircuitPython is running on. For OS/RTOS ports, this is usually an identifier of the OS, e.g. "linux". For baremetal ports it is an identifier of the chip on a board, e.g. "MicroChip SAMD51". It thus can be used to distinguish one board from another. If you need to check whether your program runs on CircuitPython (vs other Python implementation), use sys.implementation instead.


Standard error stream.


Standard input stream.


Standard output stream.


Python language version that this implementation conforms to, as a string.


Python language version that this implementation conforms to, as a tuple of ints.