I'm aware that MicroPython io documentation says

Note that for efficiency, MicroPython doesn’t provide abstract base classes corresponding to the hierarchy above, and it’s not possible to implement, or subclass, a stream class in pure Python.

Minimal example to reproduce test_stream.py:

import io

class TestStream(io.StringIO):
    def __init_(self, alloc_size):
        super().__init__(alloc_size)


test = TestStream(100)
print("Now the seg fault...")
print("hello", file=test)

$ micropython test_stream.py
Now the seg fault...
Segmentation fault: 11

But I would expect an Exception if this is not possible not a crash/seg fault.
I was able to reproduce this in unix(MacOS) and stm32(pybV1.1) ports.

Maybe is related to #1067?
I had a look at py/mpprint.c but I cannot see any hint... Is there any tool to debug these types of crashes?
This is the valgrind output:

==20210== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==20210== Using Valgrind-3.19.0.GIT-lbmacos and LibVEX; rerun with -h for copyright info
==20210== Command: micropython test_stream.py
==20210==
==20210== Warning: set address range perms: large range [0x7fff201b6000, 0x80001ffb6000) (defined)
==20210== Warning: set address range perms: large range [0x7fff201b6000, 0x7fff7fb4a000) (defined)
==20210== Warning: set address range perms: large range [0x7fff8e41a000, 0x7fffc01b6000) (noaccess)
==20210== Warning: set address range perms: large range [0x7fffc01b6000, 0x7fffe307a000) (defined)
==20210== Warning: set address range perms: large range [0x7fffe307a000, 0x7fffffe00000) (noaccess)
Now the seg fault...
==20210== Invalid read of size 1
==20210==    at 0x10002C057: ??? (in /usr/local/bin/micropython)
==20210==    by 0x10002E711: ??? (in /usr/local/bin/micropython)
==20210==    by 0x10002E7DB: ??? (in /usr/local/bin/micropython)
==20210==    by 0x10002BB4F: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100030D6F: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100023DF5: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100034D18: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100023FDE: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100078425: machine_time_pulse_us (in /usr/local/bin/micropython)
==20210==    by 0x100077DD4: machine_time_pulse_us (in /usr/local/bin/micropython)
==20210==    by 0x7FFF204DFF3C: ??? (in /dev/ttys016)
==20210==    by 0x1: ???
==20210==  Address 0x19 is not stack'd, malloc'd or (recently) free'd
==20210==
==20210==
==20210== Process terminating with default action of signal 11 (SIGSEGV)
==20210==  Access not within mapped region at address 0x19
==20210==    at 0x10002C057: ??? (in /usr/local/bin/micropython)
==20210==    by 0x10002E711: ??? (in /usr/local/bin/micropython)
==20210==    by 0x10002E7DB: ??? (in /usr/local/bin/micropython)
==20210==    by 0x10002BB4F: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100030D6F: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100023DF5: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100034D18: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100023FDE: ??? (in /usr/local/bin/micropython)
==20210==    by 0x100078425: machine_time_pulse_us (in /usr/local/bin/micropython)
==20210==    by 0x100077DD4: machine_time_pulse_us (in /usr/local/bin/micropython)
==20210==    by 0x7FFF204DFF3C: ??? (in /dev/ttys016)
==20210==    by 0x1: ???
==20210==  If you believe this happened as a result of a stack
==20210==  overflow in your program's main thread (unlikely but
==20210==  possible), you can try to increase the size of the
==20210==  main thread stack using the --main-stacksize= flag.
==20210==  The main thread stack size used in this run was 8388608.
==20210==
==20210== HEAP SUMMARY:
==20210==     in use at exit: 0 bytes in 0 blocks
==20210==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==20210==
==20210== All heap blocks were freed -- no leaks are possible
==20210==
==20210== For lists of detected and suppressed errors, rerun with: -s
==20210== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
Segmentation fault: 11

Not sure if this helps...