The Network Analyst module arcpy.na is a Python module for working with network analysis functionality provided with the ArcGIS Network Analyst エクステンション. It provides access to all the geoprocessing tools available in the Network Analyst toolbox as well as other helper functions and classes that allow you to automate the Network Analyst workflow through Python.
To accomplish your workflow, you will most likely use functions and classes from ArcPy or other modules such as the arcpy.mp module. In particular, the ArcPy Describe function can be used to access read-only properties for a network dataset or a network analysis layer.
ArcGIS Pro 2.4 provides a new module, arcpy.nax, that also allows you to perform network analysis using Python. The arcpy.na module continues to be supported, as it is useful in certain scenarios as described in Choose between the two modules.