Help with finding correct topic in Python learning

[yahya01]

Hi

I am starting at zero with Python. I need to know which topics in Python do I need to study to understand below two statements. The confusing part is more than one variable on the left side of assignment.

(x_train, y_train), (x_test, y_test) = mnist.load_data()

x_train, y_train = load_image_dataset(...)

Thanks

Regards