usys: add stubs and docs for usys module

Issue: https://github.com/pybricks/support/issues/236

doc/api/index.rst

@@ -82,6 +82,7 @@ findings on our `support page`_ so we can make Pybricks even better.
    uio
    urandom
    uselect
+   usys
 
 .. toctree::
    :maxdepth: 1

doc/api/usys.rst

@@ -0,0 +1,4 @@
+:mod:`usys` -- System specific functions
+========================================
+
+.. automodule:: usys

pyproject.toml

@@ -20,6 +20,7 @@ packages = [
     { include = "uio", from = "src" },
     { include = "urandom", from = "src" },
     { include = "uselect", from = "src" },
+    { include = "usys", from = "src" },
 ]
 
 [tool.poetry.dependencies]

src/uio/__init__.py

@@ -63,3 +63,10 @@ class StringIO:
             initial_value: Optional string object that contains initial data.
             alloc_size: Optional number of preallocated bytes.
         """
+
+
+class FileIO:
+    """
+    This is type of a file open in binary mode, e.g. using ``open(name, 'rb')``.
+    You should not instantiate this class directly.
+    """

src/usys/__init__.py

@@ -0,0 +1,40 @@
+# SPDX-License-Identifier: MIT
+# Copyright (c) 2021 The Pybricks Authors
+#
+# Portions of documentation copied from:
+# https://raw.githubusercontent.com/micropython/micropython/1e6d18c915ccea0b6a19ffec9710d33dd7e5f866/docs/library/sys.rst
+# Copyright (c) 2014-2021, Damien P. George, Paul Sokolovsky, and contributors
+
+"""
+This module provides a subset of the standard Python ``sys`` module.
+
+.. note:: This module is not available on the BOOST Move hub.
+"""
+
+from uio import FileIO
+
+# REVIST: most functions are excluded since they aren't useful for Pybricks
+
+stdin: FileIO
+"""
+Stream object that receives input from a connected terminal, if any.
+
+Writing may modify newline characters. Use ``usys.stdin.buffer`` instead if
+this is undesirable.
+
+Also see :meth:`micropython.kbd_intr` to disable ``KeyboardInterrupt`` if you
+are passing binary data via ``stdin``.
+"""
+
+stdout: FileIO
+"""
+Stream object that sends output to a connected terminal, if any.
+
+Reading may modify newline characters. Use ``usys.stdout.buffer`` instead if
+this is undesirable.
+"""
+
+stderr: FileIO
+"""
+Alias for :data:`stdout`.
+"""