How many spaces does PEP 8 stipulate that Python's first fine indentation needs to indent?

When training the network of God, we often encounter many problems. For the problem of vanishing gradient, we can choose to make. Which of the following functions to alleviate the problem?

Deep learning algorithms can be divided into supervised learning and unsupervised learning.

Principal Component Analysis (PCA) is a statistical method. Through orthogonal transformation, a set of variables that may have correlation is converted into a set of linearly related variables. The converted set of variables is called the principal component.

The following description of machine learning is correct?