Fix for weird exception raised upon starting program...

[schlopp96]

The Issue

Hello!

So during development, after extensively testing V2Mp3, no problems were found when running the application locally in a dev environment.

However, when testing the application in a typical user environment, the following exception was returned upon running V2Mp3, causing the program to immediately close:

• AttributeError: module 'typing' has no attribute '_ClassVar'. Did you mean: 'ClassVar'?

Full Traceback

Traceback (most recent call last):
  File "<pyshell#0>", line 1, in <module>
    import V2Mp3
  File "C:\Python\lib\site-packages\V2Mp3\__init__.py", line 1, in <module>
    from .main import main as v2mp3
  File "C:\Python\lib\site-packages\V2Mp3\main.pyw", line 12, in <module>
    from V2Mp3.appEvents.events import _event_loop
  File "C:\Python\lib\site-packages\V2Mp3\appEvents\events.py", line 5, in <module>
    import moviepy.editor as mv
  File "C:\Python\lib\site-packages\moviepy\editor.py", line 24, in <module>
    import imageio
  File "C:\Python\lib\site-packages\imageio\__init__.py", line 24, in <module>
    from .core import FormatManager, RETURN_BYTES
  File "C:\Python\lib\site-packages\imageio\core\__init__.py", line 16, in <module>
    from .format import Format, FormatManager
  File "C:\Python\lib\site-packages\imageio\core\format.py", line 40, in <module>
    from ..config import known_plugins, known_extensions, PluginConfig, FileExtension
  File "C:\Python\lib\site-packages\imageio\config\__init__.py", line 7, in <module>
    from .plugins import known_plugins, PluginConfig
  File "C:\Python\lib\site-packages\imageio\config\plugins.py", line 3, in <module>
    from ..core.legacy_plugin_wrapper import LegacyPlugin
  File "C:\Python\lib\site-packages\imageio\core\legacy_plugin_wrapper.py", line 5, in <module>
    from .v3_plugin_api import PluginV3, ImageProperties
  File "C:\Python\lib\site-packages\imageio\core\v3_plugin_api.py", line 9, in <module>
    class ImageProperties:
  File "C:\Python\lib\site-packages\dataclasses.py", line 958, in dataclass
    return wrap(_cls)
  File "C:\Python\lib\site-packages\dataclasses.py", line 950, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen)
  File "C:\Python\lib\site-packages\dataclasses.py", line 800, in _process_class
    cls_fields = [_get_field(cls, name, type)
  File "C:\Python\lib\site-packages\dataclasses.py", line 800, in <listcomp>
    cls_fields = [_get_field(cls, name, type)
  File "C:\Python\lib\site-packages\dataclasses.py", line 659, in _get_field
    if (_is_classvar(a_type, typing)
  File "C:\Python\lib\site-packages\dataclasses.py", line 550, in _is_classvar
    return type(a_type) is typing._ClassVar
AttributeError: module 'typing' has no attribute '_ClassVar'. Did you mean: 'ClassVar'?

Cause of Issue

• This is apparently caused by an incompatibility with the dataclasses module and certain Python versions, such as Python 3.6> as first referenced here.

• While never appearing in the V2Mp3 source code, the dataclasses module appears to be accessed by one of V2Mp3's dependencies, moviepy, which may explain why the exception occurs.

Workaround/Fix

Currently, the solution to this issue is to simply uninstall the dataclasses module if you are using Python 3.6 or above, as explained in this reply, and also here.

• To fix this issue, enter the following command in your terminal/CLI:

    pip uninstall dataclasses -y

• Once the workaround is applied, there should be no issues when running V2Mp3.