Training SolidLetters in Python 3.9.5 fails

[weshoke]

python --version
Python 3.9.5

Command:

 python .\classification.py train --dataset solidletters --dataset_path .\data\SolidLetters\ --epochs 100 --batch_size 64

Error:

Traceback (most recent call last):
  File "C:\Users\wesle\UV-Net\classification.py", line 48, in <module>
    model = Classification(num_classes=Dataset.num_classes())

[pradeep-pyro]

Fixed in #3