BUG: Access Violation error when importing PySide2 and pypylon

[Charlie-Warren]

Describe the issue:

On pypylon versions 4.1.0 and 4.2.0, if you import PySide2 before pypylon, then running EnumerateDevices crashes with no error information.

import PySide2
from pypylon import pylon

tlFactory = pylon.TlFactory.GetInstance()
devices = tlFactory.EnumerateDevices()

print("Devices: ", devices)

Therefore "Devices: ..." never gets printed, it crashes before that line.

To access a return code, I converted the above code to a string and used subprocess.run():

import sys
import subprocess

code = '''
import PySide2
from pypylon import pylon

tlFactory = pylon.TlFactory.GetInstance()
devices = tlFactory.EnumerateDevices()

print("Devices: ", devices)
'''
ret = subprocess.run([sys.executable, '-c', code])
print(ret.returncode)

This gave error code 3221225477, or 0xc0000005 in hex, an access violation error

• I tested this with the latest version of PySide2, version 5.15.2.1
• The error occurred when I used pypylon 4.1.0 and 4.2.0, but not when I used 4.0.0
• The error doesn't seem to occur if you import PySide2 after pypylon

Reproduce the code example:

import PySide2
from pypylon import pylon

tlFactory = pylon.TlFactory.GetInstance()
devices = tlFactory.EnumerateDevices()

print("Devices: ", devices)

Error message:

It crashes with no error message

Is your camera operational in Basler pylon viewer on your platform

Yes

Hardware setup & camera model(s) used

X86
Windows 10
32GB DDR4

You do not need a camera connected to encounter this error, but I used a daA1920-160um

Runtime information:

python: 3.10.0 (default, Oct 17 2021, 23:51:15) [MSC v.1929 64 bit (AMD64)]
platform: win32/AMD64/10
pypylon: 4.2.0 / 10.2.1.471

[thiesmoeller]

just to confirm. are you sure you run the script with 3.10?

there is a segfault issue with pyside2 and python >= 3.12

[Charlie-Warren]

Yes, this was with Python 3.10.0. I have also checked just now with Python 3.10.11 and the same bug appears there as well.

[Charlie-Warren]

just to confirm. are you sure you run the script with 3.10?

there is a segfault issue with pyside2 and python >= 3.12

PySide2's pypi page lists the required Python version as <3.11 so I have only been using 3.10
https://pypi.org/project/PySide2/

[thiesmoeller]

Can't reproduce tested with emulated camera and usb device.
Tested in fresh environment with uv

pyproject.toml for uv

[project]
name = "pypylon-issues-858"
version = "0.1.0"
description = "Reproduce issue"
requires-python = "==3.10.11"
dependencies = [
    "pip>=25.2",
    "pypylon>=4.2.0",
    "pyside2>=5.15.2.1",
]

Can you check on your machine in a fresh environment too?

Side note: do you need to stick to pyside2? Pyside6 has many new features

using this test_858.py

import subprocess
import sys
import platform

def run_import_order(order_name, imports):
    code = f"""
import sys
import platform

print("=== {order_name} ===")
print("Python:", sys.version.replace('\\n', ' '))
print("Platform:", platform.platform())

# Try to get versions
try:
    from pypylon import pylon
    print("pypylon version:", getattr(pylon, '__version__', 'unknown'))
except Exception as e:
    print("pypylon import failed:", e)

try:
    import PySide2
    print("PySide2 version:", getattr(PySide2, '__version__', 'unknown'))
except Exception as e:
    print("PySide2 import failed:", e)

# Execute test imports
{imports}
print("Imports executed successfully for {order_name}.")
tlFactory = pylon.TlFactory.GetInstance()
devices = tlFactory.EnumerateDevices()

print("Devices: ", devices)
"""
    print(f"\nRunning test: {order_name}")
    result = subprocess.run(
        [sys.executable, "-c", code],
        capture_output=True,
        text=True
    )
    print(result.stdout, result.returncode)
    if result.stderr.strip():
        print("stderr:\n", result.stderr)

if __name__ == "__main__":
    run_import_order(
        "Import pypylon before PySide2",
        "from pypylon import pylon\nimport PySide2\n"
    )
    run_import_order(
        "Import PySide2 before pypylon",
        "import PySide2\nfrom pypylon import pylon\n"
    )

Running test: Import pypylon before PySide2
=== Import pypylon before PySide2 ===
Python: 3.10.11 (main, May  7 2023, 18:05:05) [MSC v.1929 64 bit (AMD64)]
Platform: Windows-10-10.0.22631-SP0
pypylon version: 4.2.0
PySide2 version: 5.15.2.1
Imports executed successfully for Import pypylon before PySide2.
Devices:  (<pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' at 0x000002471E090CC0> >,)
 0

Running test: Import PySide2 before pypylon
=== Import PySide2 before pypylon ===
Python: 3.10.11 (main, May  7 2023, 18:05:05) [MSC v.1929 64 bit (AMD64)]
Platform: Windows-10-10.0.22631-SP0
pypylon version: 4.2.0
PySide2 version: 5.15.2.1
Imports executed successfully for Import PySide2 before pypylon.
Devices:  (<pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' at 0x0000021B9C1A0CC0> >,)
 0

[Charlie-Warren]

Hi there, I am using your pyproject.toml with a fresh uv environment. I don't think your test works because at this section:

# Try to get versions
try:
    from pypylon import pylon
    print("pypylon version:", getattr(pylon, '__version__', 'unknown'))
except Exception as e:
    print("pypylon import failed:", e)

try:
    import PySide2
    print("PySide2 version:", getattr(PySide2, '__version__', 'unknown'))
except Exception as e:
    print("PySide2 import failed:", e)

You are already importing pypylon first, regardless of the order later in the script. So yes test_858.py works for me, I get this output:

Running test: Import pypylon before PySide2
=== Import pypylon before PySide2 ===
Python: 3.10.11 (tags/v3.10.11:7d4cc5a, Apr  5 2023, 00:38:17) [MSC v.1929 64 bit (AMD64)]
Platform: Windows-10-10.0.19045-SP0
pypylon version: 4.2.0
PySide2 version: 5.15.2.1
Imports executed successfully for Import pypylon before PySide2.
Devices:  (<pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' at 0x0000021761210CC0> 
>, <pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' at 0x00000217612D9FB0> >)      
 0

Running test: Import PySide2 before pypylon
=== Import PySide2 before pypylon ===
Python: 3.10.11 (tags/v3.10.11:7d4cc5a, Apr  5 2023, 00:38:17) [MSC v.1929 64 bit (AMD64)]
Platform: Windows-10-10.0.19045-SP0
pypylon version: 4.2.0
PySide2 version: 5.15.2.1
Imports executed successfully for Import PySide2 before pypylon.
Devices:  (<pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' at 0x000001B394D20CC0> 
>, <pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' at 0x000001B394DE9FB0> >)      
 0

I created test_858_edit.py where I only import each package once in a try except:

import subprocess
import sys
import platform

TRY_IMPORT_PYPYLON = """
try:
    from pypylon import pylon
    print("pypylon version:", getattr(pylon, '__version__', 'unknown'))
except Exception as e:
    print("pypylon import failed:", e)
"""

TRY_IMPORT_PYSIDE2 = """
try:
    import PySide2
    print("PySide2 version:", getattr(PySide2, '__version__', 'unknown'))
except Exception as e:
    print("PySide2 import failed:", e)
"""

def run_import_order(first_import, first_import_name, second_import, second_import_name):
    code = f"""
import sys
import platform

print("=== Import {first_import_name} before {second_import_name} ===")
print("Python:", sys.version.replace('\\n', ' '))
print("Platform:", platform.platform())

# Try to get versions
{first_import}

{second_import}

print("Imports executed successfully for Import {first_import_name} before {second_import_name}.")
tlFactory = pylon.TlFactory.GetInstance()
devices = tlFactory.EnumerateDevices()

print("Devices: ", devices)
"""
    print(f"\nRunning test: Import {first_import_name} before {second_import_name}")
    result = subprocess.run(
        [sys.executable, "-c", code],
        capture_output=True,
        text=True
    )
    print(result.stdout, result.returncode)
    if result.stderr.strip():
        print("stderr:\n", result.stderr)


if __name__ == "__main__":
    run_import_order(
        TRY_IMPORT_PYPYLON,
        "pypylon",
        TRY_IMPORT_PYSIDE2,
        "PySide2",
    )
    run_import_order(
        TRY_IMPORT_PYSIDE2,
        "PySide2",
        TRY_IMPORT_PYPYLON,
        "pypylon",
    )

I get this output:

Running test: Import pypylon before PySide2
=== Import pypylon before PySide2 ===
Python: 3.10.11 (tags/v3.10.11:7d4cc5a, Apr  5 2023, 00:38:17) [MSC v.1929 64 bit (AMD64)] 
Platform: Windows-10-10.0.19045-SP0
pypylon version: 4.2.0
PySide2 version: 5.15.2.1
Imports executed successfully for Import pypylon before PySide2.
Devices:  (<pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' 
at 0x00000257B2D20BA0> >, <pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' at 0x00000257B2DE9E90> >)
 0

Running test: Import PySide2 before pypylon
 3221225477

[thiesmoeller]

can't reproduce. Fresh Windows 11 VM

Running test: Import pypylon before PySide2
=== Import pypylon before PySide2 ===
Python: 3.10.11 (main, May  7 2023, 18:05:05) [MSC v.1929 64 bit (AMD64)]
Platform: Windows-10-10.0.26200-SP0
pypylon version: 4.2.0
PySide2 version: 5.15.2.1
Imports executed successfully for Import pypylon before PySide2.
Devices:  (<pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' at 0x000002988B6A0CC0> >,)
 0

Running test: Import PySide2 before pypylon
=== Import PySide2 before pypylon ===
Python: 3.10.11 (main, May  7 2023, 18:05:05) [MSC v.1929 64 bit (AMD64)]
Platform: Windows-10-10.0.26200-SP0
PySide2 version: 5.15.2.1
pypylon version: 4.2.0
Imports executed successfully for Import PySide2 before pypylon.
Devices:  (<pypylon.pylon.DeviceInfo; proxy of <Swig Object of type 'Pylon::CDeviceInfo *' at 0x000001FE84225F50> >,)
 0
PS C:\Users\test\projects\test> 

Since I can't reproduce the error, and we know your environment uses uv in the current folder, we need to capture a call stack from the specific Python executable inside your virtual environment. This will pinpoint the exact function and module (DLL) that is failing, which is the crucial information we need.

We will use WinDbg, the modern, free debugging tool from Microsoft and your original small test script

import PySide2
from pypylon import pylon

tlFactory = pylon.TlFactory.GetInstance()
devices = tlFactory.EnumerateDevices()

print("Devices: ", devices)

Step-by-Step Guide to Capture the Call Stack

1. Install WinDbg

1. Open the Microsoft Store application on your Windows machine.
2. Search for "WinDbg".
3. Install the application published by Microsoft Corporation.

2. Find the Python Executable Path

Since you are using uv, your Python executable is located inside the virtual environment directory, which is usually named .venv (unless you customized it).

The path will look like this:
C:\Path\To\Your\Project\**\.venv\Scripts\python.exe**

You can confirm this path by running your script while the environment is active, and then checking the process properties in Task Manager, but the path above is the most likely location for a uv environment on Windows.

3. Launch Your Script in the Debugger

1. Start the WinDbg application.
2. Go to File $\rightarrow$ Launch executable (advanced).
3. Configure the launch settings:
   • Executable path: Enter the full path to the Python 3.10 executable inside your uv environment.
     • Example: C:\Path\To\Your\Project\.venv\Scripts\python.exe
   • Arguments: Enter the full path to your small, crashing Python script (e.g., C:\Path\To\Script\crashing_script.py).
   • Crucial: Check the box that says "Record debug output".
4. Click "Launch".

4. Capture the Crash Information

1. The Python script will start running inside WinDbg.
2. Allow the script to execute until the crash (segfault/access violation) occurs.
3. When the crash happens, WinDbg will halt execution and show an error message and a command prompt (usually at the bottom).
4. In the WinDbg command prompt, type the following command and press Enter:

   !analyze -v
   

5. This command runs an analysis and prints the complete crash details, including the Exception Information and the CALL STACK.

5. Share the Results

• Copy all the output generated by the !analyze -v command.
• Paste this output directly into a comment on this GitHub issue.

The output will clearly show the MODULE_NAME (the DLL responsible for the crash) and the sequence of function calls (STACK_TEXT) that led to the failure. This should allow us to identify the initialization conflict.