[Bug] Edited code on PlatformIO produces print issues, even though Pybricks tools are used.

I decided to try PlatformIO as the editor for the current CityHub project, basically to create 7 smallish modules for 1600 lines of code, rather than one massive code block. Definitely worth the effort to switch across and gaining Source Control was also a bonus.

The Pybricks compiler and uploader were set-up and hooked into keyboard shortcuts. It has worked well for the past 3 months.

[Bug]
One bug found today is with the print statement and the use of end=''
It seems the print function print(".", end='') does not print the character immediately but buffers the print instead. The code was printing one "." every 250mS during a BLE scan but the code didn't show any dots until the final print(".") was executed.

I then ran this equivalent test program on the PybricksIDE and all was well.

print("A", end="")
wait(1000)
print("B", end="")
wait(1000)
print("C", end="")
wait(1000)
print("D")

The same code on the PlatformIO fails and the ABCD prints only after the third wait(1000), and not as each print is executed.

This is the compile.BAT file in PlatformIO

@echo off

cd /d "%~dp0micropython"

set MPY="%USERPROFILE%\.platformio\penv\Lib\site-packages\mpy_cross_v6\mpy-cross.exe"

if not exist mpy mkdir mpy

%MPY% main.py -s main.py -o mpy\main.mpy
%MPY% system.py -s system.py -o mpy\system.mpy
%MPY% radio.py -s radio.py -o mpy\radio.mpy
%MPY% ports.py -s ports.py -o mpy\ports.mpy
%MPY% flash.py -s flash.py -o mpy\flash.mpy
%MPY% decoder.py -s decoder.py -o mpy\decoder.mpy
%MPY% core.py -s core.py -o mpy\core.mpy


echo.
echo ==============================
echo MPY FILE SIZES
echo ==============================

dir /-C mpy\*.mpy

exit /b 0

This is the platform.ini

; PlatformIO Project Configuration File
;
;   Build options: build flags, source filter
;   Upload options: custom upload port, speed and extra flags
;   Library options: dependencies, extra library storages
;   Advanced options: extra scripting
;
; Please visit documentation for the other options and examples
; https://docs.platformio.org/page/projectconf.html

[env:genericSTM32F413CG]
platform = ststm32
board = genericSTM32F413CG
framework = arduino

extensions.json

{
    // See http://go.microsoft.com/fwlink/?LinkId=827846
    // for the documentation about the extensions.json format
    "recommendations": [
        "platformio.platformio-ide"
    ],
    "unwantedRecommendations": [
        "ms-vscode.cpptools-extension-pack"
    ]
}

settings.json

{
    "python-envs.defaultEnvManager": "ms-python.python:system",
    "python.analysis.extraPaths": ["."],
    "python.analysis.stubPath": "./pybricks",
    "python.analysis.typeCheckingMode": "off",
    "python.analysis.diagnosticSeverityOverrides": {
        "reportMissingImports": "none",
        "reportUndefinedVariable": "none",
        "reportUnknownMemberType": "none",
        "reportUnknownArgumentType": "none",
        "reportUnknownParameterType": "none"
    }
}

tasks.json

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "Pybricks upload main.py",
            "type": "shell",
            "command": "C:\\Users\\Peter\\.platformio\\penv\\Scripts\\pybricksdev.exe",
            "args": [
                "run",
                "ble",
                "${workspaceFolder}/micropython/main.py"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "problemMatcher": "$python"
        },
        {
            "label": "Pybricks Compile Check",
            "type": "shell",
            "command": "${workspaceFolder}\\pybricks_compile_check.bat",
            "problemMatcher": [],
            "presentation": {
                "reveal": "always",
                "panel": "new",
                "showReuseMessage": false,
                "clear": true,
                "close": false
            }
        }
    ]
}

I have done the usual reboot /new batteries etc but couldn't shake the issue. Hub memory is running around 880 bytes free.

Does it make a difference if you set the PYTHONUNBUFFERED=1 environment variable when running pybricksdev?

Hi David, I tried with PYTHONUNBUFFERED=1 but no joy.

{
    "version": "2.0.1",

    "tasks": [

        {
            "label": "Pybricks upload main.py",
            "type": "shell",
            "command": "C:\\Users\\Peter\\.platformio\\penv\\Scripts\\pybricksdev.exe",

            "args": [
                "run",
                "ble",
                "${workspaceFolder}/micropython/main.py"
            ],

            "options": {
                "env": {
                    "PYTHONUNBUFFERED": "1"
                }
            },

            "group": {
                "kind": "build",
                "isDefault": true
            },

            "problemMatcher": "$python"
        },

     ]
}

I also found a similar 'non-compatibility' bug with the BLERadio and turning OFF the transmitter.

This works as expected in PybricksIDE.

from pybricks.hubs import CityHub
hub = CityHub()

from pybricks.tools import wait
from pybricks.messaging import BLERadio
radio = None

radio = BLERadio(broadcast_channel=73, observe_channels=[62])      # channels

data = 73, 48, 03, 02, 9, 8, 7
radio.broadcast(data)
wait(1000)

radio = BLERadio(broadcast_channel=None, observe_channels=[62])      # channels

The transmitter stops after sending the data.

This is the code on the PlatformIO

def Radio(value=False):
        if (value):
            radio = BLERadio(broadcast_channel=73, observe_channels=[62]) 
        else:
            radio = BLERadio(broadcast_channel=None, observe_channels=[62]) 

#elsewhere in the code....

Radio(True)                              # Transmiter ON
data = 73, 48, 03, 02, 9, 8, 7
radio.broadcast(data)
wait (200)                                 # typically 3 to 4 packets per 100mS
Radio(False)                             #Transmitter OFF

The transmitter does not stop after 200mS.

Here is the project folder for platformIO, for the original bug. You will need to edit the JSON pathnames after installing PlatformIO.

print_end_bug.zip

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[Bug] Edited code on PlatformIO produces print issues, even though Pybricks tools are used. #2791

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[Bug] Edited code on PlatformIO produces print issues, even though Pybricks tools are used. #2791

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dlech commented on Aug 21, 2026

toyotafj40 commented on Aug 21, 2026

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