Can't do import sys with ports/minimal

[yf13]

Dear experts,

it seems that I couldn't do import sys from REPL of ports/minimal following this guide.

$ make run
Use make V=1 or set BUILD_VERBOSE in your environment to increase build verbosity.
MicroPython v1.26.0-preview.232.ged38fd2f7 on 2025-07-18; minimal with unknown-cpu
>>> import sys
Traceback (most recent call last):
  File "<stdin>", in <module>
ImportError: module not found
>>> 
Exit status: 0
make: Leaving directory '/home/yf/Projects/micropython/ports/minimal'
$ file /tmp/aaa/firmware.elf
/tmp/aaa/firmware.elf: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=2d348a3a09a1ffe3f3ca6320b0443697c0a68b1f, for GNU/Linux 3.2.0, with debug_info, not stripped
 size /tmp/aaa/firmware.elf
   text	   data	    bss	    dec	    hex	filename
 149841	  11352	  26584	 187777	  2dd81	/tmp/aaa/firmware.elf

Is this intentional?

[shariltumin]

For minimal port the import will not import anything. The "main.c" file contains this:

mp_import_stat_t mp_import_stat(const char *path) {
    return MP_IMPORT_STAT_NO_EXIST;
}

The main purpose of the ports/minimal build is to test the Python interpreter. For example, you can do this:

>>> def sum(n,m):
...     print(n,'+',m,'=',n+m)
... 
>>> sum(3,4)
3 + 4 = 7

[yf13]

Thanks @shariltumin!

Given that sys is a builtin module, why this port defines MICROPY_ENABLE_EXTERNAL_IMPORT but doesn't allow any import actually?

[shariltumin]

The minimal port does not actually define mp_import_stat(). The "py/builtinimport.c" specifically mentions that this function must be provided by the port and typically uses mp_vfs_import_stat.

In this case, the MICROPY_ENABLE_EXTERNAL_IMPORT flag is irrelevant.

[agatti]

Actually, the sys module is not present because MICROPY_PY_SYS defaults to 0 when MICROPY_CONFIG_ROM_LEVEL is set to be anything below MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES.

In fact, if you add #define MICROPY_PY_SYS (1) to ports/minimal/mpconfigport.h and rebuild you'll find you can import sys all you want. It may not feature all functions/variables other ports usually have, but it is there.

[shariltumin]

What you said is absolutely true. Thanks for pointing it out!

If we have "#define MICROPY_PY_SYS (1)" "sys" module from "py/modsys.c" will be included in the firmware.

MicroPython v1.26.0-preview.386.g17fbc5abd.dirty on 2025-07-22; minimal with unknown-cpu
>>> import frozentest
uPy
a long string that is not interned
a string that has unicode αβγ chars
b'bytes 1234\x01'
123456789
0
1
2
3
>>> import sys
>>> sys.path
['', '.frozen']
>>> 

The sys module helps "py/builtinimport.c" with import by defining sys.path.

Now, a firmware that is compiled without sys, will need to use __import__.

MicroPython v1.26.0-preview.386.g17fbc5abd.dirty on 2025-07-22; minimal with unknown-cpu
>>> import sys
Traceback (most recent call last):
  File "<stdin>", in <module>
ImportError: module not found
>>> import frozentest
Traceback (most recent call last):
  File "<stdin>", in <module>
ImportError: module not found
>>> m = __import__(".frozen/frozentest")
uPy
a long string that is not interned
a string that has unicode αβγ chars
b'bytes 1234\x01'
123456789
0
1
2
3
>>>

only works for frozen module.