train_size: expected one argument

It's pretty sad when I start train with minist dataset:
python main.py --dataset mnist --train_size=28 --input_height=28 --output_height=28 --train
Then the error exist as follow:
main.py: error: argument --train_size: expected one argument
How to solve about it? Thanks!

Start in main.py and reproduce the reported command with the mnist dataset and train_size value. Inspect how the command-line arguments are handled; done means the command accepts --train_size=28 without the reported error and proceeds to training.

Written by the indexing model from the issue text.