all: Rename "sys" module to "usys".

This is consistent with the other 'micro' modules and allows implementing
additional features in Python via e.g. micropython-lib's sys.

Note this is a breaking change (not backwards compatible) for ports which
do not enable weak links, as "import sys" must now be replaced with
"import usys".

46 files changed, 142 insertions, 89 deletions

diff --git a/docs/library/index.rst b/docs/library/index.rst
index 952e67d43..43d9e87f3 100644
--- a/docs/library/index.rst
+++ b/docs/library/index.rst
@@ -77,7 +77,6 @@ it will fallback to loading the built-in ``ujson`` module.
    cmath.rst
    gc.rst
    math.rst
-   sys.rst
    uarray.rst
    uasyncio.rst
    ubinascii.rst
@@ -93,6 +92,7 @@ it will fallback to loading the built-in ``ujson`` module.
    usocket.rst
    ussl.rst
    ustruct.rst
+   usys.rst
    utime.rst
    uzlib.rst
    _thread.rst
diff --git a/docs/library/sys.rst b/docs/library/usys.rst
index 24f9e353b..960164385 100644
--- a/docs/library/sys.rst
+++ b/docs/library/usys.rst
@@ -1,7 +1,7 @@
-:mod:`sys` -- system specific functions
-=======================================
+:mod:`usys` -- system specific functions
+========================================
 
-.. module:: sys
+.. module:: usys
    :synopsis: system specific functions
 
 |see_cpython_module| :mod:`python:sys`.
@@ -28,10 +28,10 @@ Functions
       This function is a MicroPython extension intended to provide similar
       functionality to the :mod:`atexit` module in CPython.
 
-.. function:: print_exception(exc, file=sys.stdout, /)
+.. function:: print_exception(exc, file=usys.stdout, /)
 
    Print exception with a traceback to a file-like object *file* (or
-   `sys.stdout` by default).
+   `usys.stdout` by default).
 
    .. admonition:: Difference to CPython
       :class: attention
@@ -84,7 +84,7 @@ Constants
    value directly, but instead count number of bits in it::
 
     bits = 0
-    v = sys.maxsize
+    v = usys.maxsize
     while v:
         bits += 1
         v >>= 1
@@ -113,7 +113,7 @@ Constants
    is an identifier of a board, e.g. ``"pyboard"`` for the original MicroPython
    reference board. It thus can be used to distinguish one board from another.
    If you need to check whether your program runs on MicroPython (vs other
-   Python implementation), use `sys.implementation` instead.
+   Python implementation), use `usys.implementation` instead.
 
 .. data:: stderr
 
diff --git a/drivers/nrf24l01/nrf24l01test.py b/drivers/nrf24l01/nrf24l01test.py
index 14efbffd2..56bdb6e26 100644
--- a/drivers/nrf24l01/nrf24l01test.py
+++ b/drivers/nrf24l01/nrf24l01test.py
@@ -1,6 +1,6 @@
 """Test for nrf24l01 module.  Portable between MicroPython targets."""
 
-import sys
+import usys
 import ustruct as struct
 import utime
 from machine import Pin, SPI
@@ -14,14 +14,14 @@ _RX_POLL_DELAY = const(15)
 # master may be a slow device. Value tested with Pyboard, ESP32 and ESP8266.
 _SLAVE_SEND_DELAY = const(10)
 
-if sys.platform == "pyboard":
+if usys.platform == "pyboard":
     cfg = {"spi": 2, "miso": "Y7", "mosi": "Y8", "sck": "Y6", "csn": "Y5", "ce": "Y4"}
-elif sys.platform == "esp8266":  # Hardware SPI
+elif usys.platform == "esp8266":  # Hardware SPI
     cfg = {"spi": 1, "miso": 12, "mosi": 13, "sck": 14, "csn": 4, "ce": 5}
-elif sys.platform == "esp32":  # Software SPI
+elif usys.platform == "esp32":  # Software SPI
     cfg = {"spi": -1, "miso": 32, "mosi": 33, "sck": 25, "csn": 26, "ce": 27}
 else:
-    raise ValueError("Unsupported platform {}".format(sys.platform))
+    raise ValueError("Unsupported platform {}".format(usys.platform))
 
 # Addresses are in little-endian format. They correspond to big-endian
 # 0xf0f0f0f0e1, 0xf0f0f0f0d2
diff --git a/extmod/webrepl/websocket_helper.py b/extmod/webrepl/websocket_helper.py
index 5ca80534e..3260acc52 100644
--- a/extmod/webrepl/websocket_helper.py
+++ b/extmod/webrepl/websocket_helper.py
@@ -1,4 +1,7 @@
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 
 try:
     import ubinascii as binascii
diff --git a/py/objmodule.c b/py/objmodule.c
index 060e1bc1e..a1f9d9d7f 100644
--- a/py/objmodule.c
+++ b/py/objmodule.c
@@ -159,7 +159,7 @@ STATIC const mp_rom_map_elem_t mp_builtin_module_table[] = {
     #endif
     #endif
     #if MICROPY_PY_SYS
-    { MP_ROM_QSTR(MP_QSTR_sys), MP_ROM_PTR(&mp_module_sys) },
+    { MP_ROM_QSTR(MP_QSTR_usys), MP_ROM_PTR(&mp_module_sys) },
     #endif
     #if MICROPY_PY_GC && MICROPY_ENABLE_GC
     { MP_ROM_QSTR(MP_QSTR_gc), MP_ROM_PTR(&mp_module_gc) },
diff --git a/tests/basics/async_await2.py b/tests/basics/async_await2.py
index 1e3164df9..56f77604a 100644
--- a/tests/basics/async_await2.py
+++ b/tests/basics/async_await2.py
@@ -1,6 +1,9 @@
 # test await expression
 
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 if sys.implementation.name == 'micropython':
     # uPy allows normal generators to be awaitables
     coroutine = lambda f: f
diff --git a/tests/basics/async_for2.py b/tests/basics/async_for2.py
index aad23a3e5..4af3be4c6 100644
--- a/tests/basics/async_for2.py
+++ b/tests/basics/async_for2.py
@@ -1,6 +1,9 @@
 # test waiting within "async for" __anext__ function
 
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 if sys.implementation.name == 'micropython':
     # uPy allows normal generators to be awaitables
     coroutine = lambda f: f
diff --git a/tests/basics/async_with2.py b/tests/basics/async_with2.py
index 44421ae91..4dd138624 100644
--- a/tests/basics/async_with2.py
+++ b/tests/basics/async_with2.py
@@ -1,6 +1,9 @@
 # test waiting within async with enter/exit functions
 
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 if sys.implementation.name == 'micropython':
     # uPy allows normal generators to be awaitables
     coroutine = lambda f: f
diff --git a/tests/basics/attrtuple1.py b/tests/basics/attrtuple1.py
index 78a0fbed1..249c030bb 100644
--- a/tests/basics/attrtuple1.py
+++ b/tests/basics/attrtuple1.py
@@ -1,7 +1,10 @@
 # test attrtuple
 # we can't test this type directly so we use sys.implementation object
 
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 t = sys.implementation
 
 # It can be just a normal tuple on small ports
diff --git a/tests/basics/builtin_callable.py b/tests/basics/builtin_callable.py
index 3ae49f004..c0a9d0c47 100644
--- a/tests/basics/builtin_callable.py
+++ b/tests/basics/builtin_callable.py
@@ -7,7 +7,10 @@ print(callable([]))
 print(callable("dfsd"))
 
 # modules should not be callabe
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 print(callable(sys))
 
 # builtins should be callable
diff --git a/tests/basics/builtin_dir.py b/tests/basics/builtin_dir.py
index 1eecbd044..1f2b498d7 100644
--- a/tests/basics/builtin_dir.py
+++ b/tests/basics/builtin_dir.py
@@ -4,7 +4,10 @@
 print('__name__' in dir())
 
 # dir of module
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 print('version' in dir(sys))
 
 # dir of type
diff --git a/tests/basics/int_big1.py b/tests/basics/int_big1.py
index 40d16c455..108e3ee5c 100644
--- a/tests/basics/int_big1.py
+++ b/tests/basics/int_big1.py
@@ -102,7 +102,10 @@ x = 4611686018427387904 # big
 x = -4611686018427387904 # big
 
 # sys.maxsize is a constant mpz, so test it's compatible with dynamic ones
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 print(sys.maxsize + 1 - 1 == sys.maxsize)
 
 # test extraction of big int value via mp_obj_get_int_maybe
diff --git a/tests/basics/module2.py b/tests/basics/module2.py
index a13560157..5923a27e0 100644
--- a/tests/basics/module2.py
+++ b/tests/basics/module2.py
@@ -1,6 +1,6 @@
 # uPy behaviour only: builtin modules are read-only
-import sys
+import usys
 try:
-    sys.x = 1
+    usys.x = 1
 except AttributeError:
     print("AttributeError")
diff --git a/tests/basics/python34.py b/tests/basics/python34.py
index 4030db143..0f6e4bafd 100644
--- a/tests/basics/python34.py
+++ b/tests/basics/python34.py
@@ -33,9 +33,9 @@ test_syntax("del ()") # can't delete empty tuple (in 3.6 we can)
 
 # from basics/sys1.py
 # uPy prints version 3.4
-import sys
-print(sys.version[:3])
-print(sys.version_info[0], sys.version_info[1])
+import usys
+print(usys.version[:3])
+print(usys.version_info[0], usys.version_info[1])
 
 # from basics/exception1.py
 # in 3.7 no comma is printed if there is only 1 arg (in 3.4-3.6 one is printed)
diff --git a/tests/basics/string_compare.py b/tests/basics/string_compare.py
index 6515809b3..f34879df2 100644
--- a/tests/basics/string_compare.py
+++ b/tests/basics/string_compare.py
@@ -51,7 +51,10 @@ print("1/" <= "1")
 
 # this tests an internal string that doesn't have a hash with a string
 # that does have a hash, but the lengths of the two strings are different
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 print(sys.version == 'a long string that has a hash')
 
 # this special string would have a hash of 0 but is incremented to 1
diff --git a/tests/basics/sys1.py b/tests/basics/sys1.py
index 095824afa..0947ea196 100644
--- a/tests/basics/sys1.py
+++ b/tests/basics/sys1.py
@@ -1,6 +1,9 @@
 # test sys module
 
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 
 print(sys.__name__)
 print(type(sys.path))
diff --git a/tests/basics/sys_exit.py b/tests/basics/sys_exit.py
index b1f71549d..4d640ae60 100644
--- a/tests/basics/sys_exit.py
+++ b/tests/basics/sys_exit.py
@@ -1,6 +1,9 @@
 # test sys module's exit function
 
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 
 try:
     sys.exit
diff --git a/tests/basics/sys_getsizeof.py b/tests/basics/sys_getsizeof.py
index fe1b403e0..4dc919848 100644
--- a/tests/basics/sys_getsizeof.py
+++ b/tests/basics/sys_getsizeof.py
@@ -1,6 +1,9 @@
 # test sys.getsizeof() function
 
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 try:
     sys.getsizeof
 except AttributeError:
diff --git a/tests/extmod/uctypes_array_assign_native_le.py b/tests/extmod/uctypes_array_assign_native_le.py
index d4c27fc4b..5bddfcdf2 100644
--- a/tests/extmod/uctypes_array_assign_native_le.py
+++ b/tests/extmod/uctypes_array_assign_native_le.py
@@ -1,4 +1,4 @@
-import sys
+import usys
 
 try:
     import uctypes
@@ -6,7 +6,7 @@ except ImportError:
     print("SKIP")
     raise SystemExit
 
-if sys.byteorder != "little":
+if usys.byteorder != "little":
     print("SKIP")
     raise SystemExit
 
diff --git a/tests/extmod/uctypes_array_assign_native_le_intbig.py b/tests/extmod/uctypes_array_assign_native_le_intbig.py
index f33c63b4e..42583b8af 100644
--- a/tests/extmod/uctypes_array_assign_native_le_intbig.py
+++ b/tests/extmod/uctypes_array_assign_native_le_intbig.py
@@ -1,4 +1,4 @@
-import sys
+import usys
 
 try:
     import uctypes
@@ -6,7 +6,7 @@ except ImportError:
     print("SKIP")
     raise SystemExit
 
-if sys.byteorder != "little":
+if usys.byteorder != "little":
     print("SKIP")
     raise SystemExit
 
diff --git a/tests/extmod/uctypes_native_le.py b/tests/extmod/uctypes_native_le.py
index 7958e5c22..9889b98e9 100644
--- a/tests/extmod/uctypes_native_le.py
+++ b/tests/extmod/uctypes_native_le.py
@@ -1,7 +1,7 @@
 # This test is exactly like uctypes_le.py, but uses native structure layout.
 # Codepaths for packed vs native structures are different. This test only works
 # on little-endian machine (no matter if 32 or 64 bit).
-import sys
+import usys
 
 try:
     import uctypes
@@ -9,7 +9,7 @@ except ImportError:
     print("SKIP")
     raise SystemExit
 
-if sys.byteorder != "little":
+if usys.byteorder != "little":
     print("SKIP")
     raise SystemExit
 
diff --git a/tests/extmod/uctypes_ptr_le.py b/tests/extmod/uctypes_ptr_le.py
index 5d8094ee4..f475465ae 100644
--- a/tests/extmod/uctypes_ptr_le.py
+++ b/tests/extmod/uctypes_ptr_le.py
@@ -1,4 +1,4 @@
-import sys
+import usys
 
 try:
     import uctypes
@@ -6,7 +6,7 @@ except ImportError:
     print("SKIP")
     raise SystemExit
 
-if sys.byteorder != "little":
+if usys.byteorder != "little":
     print("SKIP")
     raise SystemExit
 
diff --git a/tests/extmod/uctypes_ptr_native_le.py b/tests/extmod/uctypes_ptr_native_le.py
index 8ca4d2c55..ca2b316c5 100644
--- a/tests/extmod/uctypes_ptr_native_le.py
+++ b/tests/extmod/uctypes_ptr_native_le.py
@@ -1,4 +1,4 @@
-import sys
+import usys
 
 try:
     import uctypes
@@ -6,7 +6,7 @@ except ImportError:
     print("SKIP")
     raise SystemExit
 
-if sys.byteorder != "little":
+if usys.byteorder != "little":
     print("SKIP")
     raise SystemExit
 
diff --git a/tests/extmod/vfs_fat_more.py b/tests/extmod/vfs_fat_more.py
index d8449829d..076802f6a 100644
--- a/tests/extmod/vfs_fat_more.py
+++ b/tests/extmod/vfs_fat_more.py
@@ -111,10 +111,10 @@ print(uos.listdir())
 print(uos.listdir("sys"))
 
 # test importing a file from a mounted FS
-import sys
+import usys
 
-sys.path.clear()
-sys.path.append("/sys")
+usys.path.clear()
+usys.path.append("/sys")
 with open("sys/test_module.py", "w") as f:
     f.write('print("test_module!")')
 import test_module
diff --git a/tests/extmod/vfs_lfs_mount.py b/tests/extmod/vfs_lfs_mount.py
index 9207f4a8c..2c40b2989 100644
--- a/tests/extmod/vfs_lfs_mount.py
+++ b/tests/extmod/vfs_lfs_mount.py
@@ -68,17 +68,17 @@ def test(bdev, vfs_class):
     uos.umount("/lfs")
 
     # clear imported modules
-    sys.modules.clear()
+    usys.modules.clear()
 
 
 bdev = RAMBlockDevice(30)
 
 # initialise path
-import sys
+import usys
 
-sys.path.clear()
-sys.path.append("/lfs")
-sys.path.append("")
+usys.path.clear()
+usys.path.append("/lfs")
+usys.path.append("")
 
 # run tests
 test(bdev, uos.VfsLfs1)
diff --git a/tests/extmod/vfs_userfs.py b/tests/extmod/vfs_userfs.py
index 3cdfe82ee..570b83353 100644
--- a/tests/extmod/vfs_userfs.py
+++ b/tests/extmod/vfs_userfs.py
@@ -1,7 +1,7 @@
 # test VFS functionality with a user-defined filesystem
 # also tests parts of uio.IOBase implementation
 
-import sys
+import usys
 
 try:
     import uio
@@ -76,9 +76,9 @@ f = open("/userfs/data.txt")
 print(f.read())
 
 # import files from the user filesystem
-sys.path.append("/userfs")
+usys.path.append("/userfs")
 import usermod1
 
 # unmount and undo path addition
 uos.umount("/userfs")
-sys.path.pop()
+usys.path.pop()
diff --git a/tests/feature_check/byteorder.py b/tests/feature_check/byteorder.py
index c82a41a24..509bd8b1b 100644
--- a/tests/feature_check/byteorder.py
+++ b/tests/feature_check/byteorder.py
@@ -1,3 +1,6 @@
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 
 print(sys.byteorder)
diff --git a/tests/float/float2int_doubleprec_intbig.py b/tests/float/float2int_doubleprec_intbig.py
index 84fa2d253..418eddb60 100644
--- a/tests/float/float2int_doubleprec_intbig.py
+++ b/tests/float/float2int_doubleprec_intbig.py
@@ -2,10 +2,10 @@
 
 try:
     import ustruct as struct
+    import usys as sys
 except:
     import struct
-
-import sys
+    import sys
 
 maxsize_bits = 0
 maxsize = sys.maxsize
diff --git a/tests/float/float2int_fp30_intbig.py b/tests/float/float2int_fp30_intbig.py
index 75ff52f39..fcbe2e309 100644
--- a/tests/float/float2int_fp30_intbig.py
+++ b/tests/float/float2int_fp30_intbig.py
@@ -2,10 +2,10 @@
 
 try:
     import ustruct as struct
+    import usys as sys
 except:
     import struct
-
-import sys
+    import sys
 
 maxsize_bits = 0
 maxsize = sys.maxsize
diff --git a/tests/float/float2int_intbig.py b/tests/float/float2int_intbig.py
index 62aca3963..865aeea7b 100644
--- a/tests/float/float2int_intbig.py
+++ b/tests/float/float2int_intbig.py
@@ -2,10 +2,10 @@
 
 try:
     import ustruct as struct
+    import usys as sys
 except:
     import struct
-
-import sys
+    import sys
 
 maxsize_bits = 0
 maxsize = sys.maxsize
diff --git a/tests/io/argv.py b/tests/io/argv.py
index 53254da11..834292504 100644
--- a/tests/io/argv.py
+++ b/tests/io/argv.py
@@ -1,3 +1,6 @@
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 
 print(sys.argv)
diff --git a/tests/io/builtin_print_file.py b/tests/io/builtin_print_file.py
index 822356a6c..e5c20b64e 100644
--- a/tests/io/builtin_print_file.py
+++ b/tests/io/builtin_print_file.py
@@ -1,6 +1,9 @@
 # test builtin print function, using file= argument
 
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 
 try:
     sys.stdout
diff --git a/tests/io/file_stdio.py b/tests/io/file_stdio.py
index cbdb07016..6c08f35d7 100644
--- a/tests/io/file_stdio.py
+++ b/tests/io/file_stdio.py
@@ -1,4 +1,7 @@
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 
 print(sys.stdin.fileno())
 print(sys.stdout.fileno())
diff --git a/tests/io/resource_stream.py b/tests/io/resource_stream.py
index 5656205b6..b589ff99b 100644
--- a/tests/io/resource_stream.py
+++ b/tests/io/resource_stream.py
@@ -1,5 +1,5 @@
 import uio
-import sys
+import usys
 
 try:
     uio.resource_stream
@@ -11,5 +11,5 @@ buf = uio.resource_stream("data", "file2")
 print(buf.read())
 
 # resource_stream(None, ...) look ups from current dir, hence sys.path[0] hack
-buf = uio.resource_stream(None, sys.path[0] + "/data/file2")
+buf = uio.resource_stream(None, usys.path[0] + "/data/file2")
 print(buf.read())
diff --git a/tests/micropython/emg_exc.py b/tests/micropython/emg_exc.py
index bca4d2d9f..b8df94b07 100644
--- a/tests/micropython/emg_exc.py
+++ b/tests/micropython/emg_exc.py
@@ -1,7 +1,7 @@
 # test that emergency exceptions work
 
 import micropython
-import sys
+import usys
 
 try:
     import uio
@@ -26,7 +26,7 @@ def f():
 
     # print the exception
     buf = uio.StringIO()
-    sys.print_exception(exc, buf)
+    usys.print_exception(exc, buf)
     for l in buf.getvalue().split("\n"):
         if l.startswith("  File "):
             print(l.split('"')[2])
diff --git a/tests/micropython/heapalloc_traceback.py b/tests/micropython/heapalloc_traceback.py
index eabd09388..09a2ad2c1 100644
--- a/tests/micropython/heapalloc_traceback.py
+++ b/tests/micropython/heapalloc_traceback.py
@@ -1,7 +1,7 @@
 # test that we can generate a traceback without allocating
 
 import micropython
-import sys
+import usys
 
 try:
     import uio
@@ -33,7 +33,7 @@ test()
 
 # print the exception that was raised
 buf = uio.StringIO()
-sys.print_exception(global_exc, buf)
+usys.print_exception(global_exc, buf)
 for l in buf.getvalue().split("\n"):
     # uPy on pyboard prints <stdin> as file, so remove filename.
     if l.startswith("  File "):
diff --git a/tests/micropython/import_mpy_invalid.py b/tests/micropython/import_mpy_invalid.py
index 00973fe3f..02fd4b125 100644
--- a/tests/micropython/import_mpy_invalid.py
+++ b/tests/micropython/import_mpy_invalid.py
@@ -1,7 +1,7 @@
 # test importing of invalid .mpy files
 
 try:
-    import sys, uio, uos
+    import usys, uio, uos
 
     uio.IOBase
     uos.mount
@@ -54,7 +54,7 @@ user_files = {
 
 # create and mount a user filesystem
 uos.mount(UserFS(user_files), "/userfs")
-sys.path.append("/userfs")
+usys.path.append("/userfs")
 
 # import .mpy files from the user filesystem
 for i in range(len(user_files)):
@@ -66,4 +66,4 @@ for i in range(len(user_files)):
 
 # unmount and undo path addition
 uos.umount("/userfs")
-sys.path.pop()
+usys.path.pop()
diff --git a/tests/micropython/import_mpy_native_x64.py b/tests/micropython/import_mpy_native_x64.py
index d0de507d4..3e7b2058e 100644
--- a/tests/micropython/import_mpy_native_x64.py
+++ b/tests/micropython/import_mpy_native_x64.py
@@ -1,7 +1,7 @@
 # test importing of .mpy files with native code (x64 only)
 
 try:
-    import sys, uio, uos
+    import usys, uio, uos
 
     uio.IOBase
     uos.mount
@@ -9,7 +9,7 @@ except (ImportError, AttributeError):
     print("SKIP")
     raise SystemExit
 
-if not (sys.platform == "linux" and sys.maxsize > 2 ** 32):
+if not (usys.platform == "linux" and usys.maxsize > 2 ** 32):
     print("SKIP")
     raise SystemExit
 
@@ -101,7 +101,7 @@ user_files = {
 
 # create and mount a user filesystem
 uos.mount(UserFS(user_files), "/userfs")
-sys.path.append("/userfs")
+usys.path.append("/userfs")
 
 # import .mpy files from the user filesystem
 for i in range(len(user_files)):
@@ -114,4 +114,4 @@ for i in range(len(user_files)):
 
 # unmount and undo path addition
 uos.umount("/userfs")
-sys.path.pop()
+usys.path.pop()
diff --git a/tests/micropython/opt_level_lineno.py b/tests/micropython/opt_level_lineno.py
index d8253e54b..1cbf2fb1a 100644
--- a/tests/micropython/opt_level_lineno.py
+++ b/tests/micropython/opt_level_lineno.py
@@ -3,4 +3,4 @@ import micropython as micropython
 # check that level 3 doesn't store line numbers
 # the expected output is that any line is printed as "line 1"
 micropython.opt_level(3)
-exec("try:\n xyz\nexcept NameError as er:\n import sys\n sys.print_exception(er)")
+exec("try:\n xyz\nexcept NameError as er:\n import usys\n usys.print_exception(er)")
diff --git a/tests/micropython/viper_misc_intbig.py b/tests/micropython/viper_misc_intbig.py
index 055c08d8e..eda873ca6 100644
--- a/tests/micropython/viper_misc_intbig.py
+++ b/tests/micropython/viper_misc_intbig.py
@@ -6,6 +6,6 @@ def viper_uint() -> uint:
     return uint(-1)
 
 
-import sys
+import usys
 
-print(viper_uint() == (sys.maxsize << 1 | 1))
+print(viper_uint() == (usys.maxsize << 1 | 1))
diff --git a/tests/misc/print_exception.py b/tests/misc/print_exception.py
index f26c1fd5a..9b3467b0a 100644
--- a/tests/misc/print_exception.py
+++ b/tests/misc/print_exception.py
@@ -1,10 +1,10 @@
-import sys
-
 try:
     try:
         import uio as io
+        import usys as sys
     except ImportError:
         import io
+        import sys
 except ImportError:
     print("SKIP")
     raise SystemExit
diff --git a/tests/misc/sys_atexit.py b/tests/misc/sys_atexit.py
index e9c5693f9..141b24cc9 100644
--- a/tests/misc/sys_atexit.py
+++ b/tests/misc/sys_atexit.py
@@ -1,9 +1,9 @@
 # test sys.atexit() function
 
-import sys
+import usys
 
 try:
-    sys.atexit
+    usys.atexit
 except AttributeError:
     print("SKIP")
     raise SystemExit
@@ -15,7 +15,7 @@ def do_at_exit():
     print("done at exit:", some_var)
 
 
-sys.atexit(do_at_exit)
+usys.atexit(do_at_exit)
 
 some_var = "ok"
 print("done before exit")
diff --git a/tests/misc/sys_exc_info.py b/tests/misc/sys_exc_info.py
index d7e8a2d94..3a8c4a6c8 100644
--- a/tests/misc/sys_exc_info.py
+++ b/tests/misc/sys_exc_info.py
@@ -1,4 +1,7 @@
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 
 try:
     sys.exc_info
diff --git a/tests/run-natmodtests.py b/tests/run-natmodtests.py
index f88ca0b78..8eb27169c 100755
--- a/tests/run-natmodtests.py
+++ b/tests/run-natmodtests.py
@@ -30,7 +30,7 @@ TEST_MAPPINGS = {
 
 # Code to allow a target MicroPython to import an .mpy from RAM
 injected_import_hook_code = """\
-import sys, uos, uio
+import usys, uos, uio
 class __File(uio.IOBase):
   def __init__(self):
     self.off = 0
@@ -54,7 +54,7 @@ class __FS:
     return __File()
 uos.mount(__FS(), '/__remote')
 uos.chdir('/__remote')
-sys.modules['{}'] = __import__('__injected')
+usys.modules['{}'] = __import__('__injected')
 """
 
 
diff --git a/tests/run-tests-exp.py b/tests/run-tests-exp.py
index 34c6f650f..ac32fe986 100644
--- a/tests/run-tests-exp.py
+++ b/tests/run-tests-exp.py
@@ -5,7 +5,7 @@
 # This script is intended to be run by the same interpreter executable
 # which is to be tested, so should use minimal language functionality.
 #
-import sys
+import usys as sys
 import uos as os
 
 
diff --git a/tests/thread/thread_stacksize1.py b/tests/thread/thread_stacksize1.py
index 5827237a1..5d25509b7 100644
--- a/tests/thread/thread_stacksize1.py
+++ b/tests/thread/thread_stacksize1.py
@@ -1,8 +1,10 @@
 # test setting the thread stack size
 #
 # MIT license; Copyright (c) 2016 Damien P. George on behalf of Pycom Ltd
-
-import sys
+try:
+    import usys as sys
+except ImportError:
+    import sys
 import _thread
 
 # different implementations have different minimum sizes