QUERY · ISSUE

mpremote cat hangs on Windows interactive console with Unicode content

openby Josverlopened 2026-01-07updated 2026-01-09

bugtoolsunicode

Port, board and/or hardware

Host Windows (any hardware)

MicroPython version

mpremote 1.27.0

Reproduction

On Windows, have a MicroPython device with a file containing Unicode text:
```
/unicode_test/नेपाली_नाम.txt
```
Run mpremote cat interactively in PowerShell (NOT piped or captured):
```
mpremote cat :/unicode_test/नेपाली_नाम.txt
```
The command hangs indefinitely. Even with PYTHONIOENCODING=utf-8 set, it still hangs.
Press Ctrl-C to interrupt.

Observations

The same command works correctly when:

Output is piped: mpremote cat :file.txt > output.txt
Output is captured by subprocess: subprocess.run([...], capture_output=True)
Running on Linux (even in WSL2 on the same machine)

The hang ONLY occurs when stdout is a real Windows console (isatty=True).

Expected behaviour

$ mpremote cat :/unicode_test/नेपाली_नाम.txt

Nepali Name - नेपाली नाम

This file tests Nepali (Devanagari) script.

Script: Devanagari (Nepali variant)

Vowels: अ आ इ ई उ ऊ ऋ ए ऐ ओ औ
Consonants: क ख ग घ ङ च छ ज झ ञ ट ठ ड ढ ण त थ द ध न
...



for test files see : [https://github.com/[Josverl/unicode_mpy](https://github.com/Josverl/unicode_mpy)

https://github.com/Josverl/unicode_mpy/tree/main/test_data/South_Asian_Indic


### Observed behaviour

The command hangs indefinitely when run interactively on Windows with Unicode content. Ctrl-C shows the following traceback:

Traceback (most recent call last):
File "...\mpremote\main.py", line 614, in main
handler_func(state, args)
File "...\mpremote\commands.py", line 421, in do_filesystem
state.transport.fs_printfile(path)
File "...\mpremote\transport.py", line 129, in fs_printfile
self.exec(cmd, data_consumer=stdout_write_bytes)
File "...\mpremote\transport_serial.py", line 309, in exec
ret, ret_err = self.exec_raw(command, data_consumer=data_consumer)
File "...\mpremote\transport_serial.py", line 296, in exec_raw
return self.follow(timeout, data_consumer)
File "...\mpremote\transport_serial.py", line 204, in follow
data = self.read_until(1, b"\x04", timeout=timeout, data_consumer=data_consumer)
File "...\mpremote\transport_serial.py", line 146, in read_until
data_consumer(new_data)
File "...\mpremote\transport.py", line 36, in stdout_write_bytes
sys.stdout.buffer.flush()
KeyboardInterrupt


### Additional Information


**Initial hypothesis (DISPROVEN):** The hang was suspected to be in `stdout_write_bytes()`:
```python
def stdout_write_bytes(b):
    sys.stdout.buffer.write(b)
    sys.stdout.buffer.flush()  # <-- Suspected to hang

Test result: A standalone Python script calling sys.stdout.buffer.write() + flush() with identical Unicode content does NOT hang.

Actual cause: The hang is NOT in CPython's stdout handling. The issue is elsewhere in mpremote, possibly:

Different code path when stdout.isatty() is True vs False
Threading/synchronization issues between reader/writer threads
Windows console API interaction issues
Serial/socket transport blocking behavior

Possibly Related Issues

https://github.com/micropython/micropython/issues/15228 - Unable to print unicode characters when running repl with mpremote

Code of Conduct

Yes, I agree

CANDIDATE · ISSUE

`mpremote mip install` hangs when uploading files

openby agattiopened 2025-11-23updated 2025-11-25

bugport-stm32

Port, board and/or hardware

STM32 port on a NUCLEO-144--F767ZI

MicroPython version

MicroPython v1.27.0-preview.440.ga6864109db on 2025-11-23; NUCLEO-F767ZI with STM32F767

Reproduction

(Optional) Perform a mass erase on all flash blocks.
Build main firmware and mboot, then upload image to the board with deploy-stlink
Reboot the board
Run mpremote mip install unittest
Wait until it hangs

Expected behaviour

mpremote mip should install the required package

Observed behaviour

The upload process hangs at random intervals, and when stopping it via CTRL+C the traceback is as follows (the process was stopped after a few minutes of being stuck at 13%):

Traceback (most recent call last):
  File "/home/agatti/src/micropython/ports/stm32/../../tools/mpremote/mpremote.py", line 6, in <module>
    sys.exit(main.main())
             ~~~~~~~~~^^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/main.py", line 614, in main
    handler_func(state, args)
    ~~~~~~~~~~~~^^^^^^^^^^^^^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/mip.py", line 206, in do_mip
    _install_package(
    ~~~~~~~~~~~~~~~~^
        state.transport,
        ^^^^^^^^^^^^^^^^
    ...<4 lines>...
        args.mpy,
        ^^^^^^^^^
    )
    ^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/mip.py", line 169, in _install_package
    _install_json(transport, package, index, target, version, mpy)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/mip.py", line 131, in _install_json
    _download_file(transport, file_url, fs_target_path)
    ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/mip.py", line 99, in _download_file
    transport.fs_writefile(dest, data, progress_callback=show_progress_bar)
    ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/transport.py", line 163, in fs_writefile
    self.exec("w(" + repr(chunk) + ")")
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/transport_serial.py", line 309, in exec
    ret, ret_err = self.exec_raw(command, data_consumer=data_consumer)
                   ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/transport_serial.py", line 295, in exec_raw
    self.exec_raw_no_follow(command)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/transport_serial.py", line 273, in exec_raw_no_follow
    return self.raw_paste_write(command_bytes)
           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
  File "/home/agatti/src/micropython/tools/mpremote/mpremote/transport_serial.py", line 228, in raw_paste_write
    data = self.serial.read(1)
  File "/usr/lib/python3.13/site-packages/serial/serialposix.py", line 565, in read
    ready, _, _ = select.select([self.fd, self.pipe_abort_read_r], [], [], timeout.time_left())
                  ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
KeyboardInterrupt

The firmware is still waiting for data to arrive on the serial port when mpremote seems to be stuck:

^C
Program received signal SIGINT, Interrupt.
mp_hal_stdin_rx_chr () at mphalport.c:53
53          for (;;) {
08:14:08 mp_hal_stdin_rx_chr > bt
#0  mp_hal_stdin_rx_chr () at mphalport.c:53
#1  0x08068aec in mp_reader_stdin_readbyte (data=0x2007ff74)
    at ../../shared/runtime/pyexec.c:255
#2  0x08023164 in next_char (lex=lex@entry=0x20037b50) at ../../py/lexer.c:174
#3  0x08023456 in parse_string_literal (lex=0x20037b50, is_raw=false, 
    is_fstring=false) at ../../py/lexer.c:413
#4  mp_lexer_to_next (lex=lex@entry=0x20037b50) at ../../py/lexer.c:696
#5  0x0802443c in mp_parse (lex=lex@entry=0x20037b50, 
    input_kind=input_kind@entry=MP_PARSE_FILE_INPUT) at ../../py/parse.c:1167
#6  0x08068be8 in parse_compile_execute (source=source@entry=0x2007ff7c, 
    input_kind=input_kind@entry=MP_PARSE_FILE_INPUT, 
    exec_flags=exec_flags@entry=65) at ../../shared/runtime/pyexec.c:111
#7  0x08068d90 in do_reader_stdin (c=65) at ../../shared/runtime/pyexec.c:324
#8  pyexec_raw_repl () at ../../shared/runtime/pyexec.c:567
#9  0x080730d4 in stm32_main (reset_mode=<optimized out>) at main.c:718
#10 <signal handler called>

in fact, reconnecting to the serial port will find the interpreter still waiting for data to arrive.

Additional Information

No, I've provided everything above.

Code of Conduct

Yes, I agree