import bpy  # in design it is _bpy

bpy.utils.log.error("err hello")
bpy.utils.log.warning("warn hello")
bpy.utils.log.info("info hello")
bpy.utils.log.debug("debug hello")

# ----
import logging
import bpy
log = logging.getLogger("bpy.my_addon")  # add type for easy filtering in blender
log.addHandler(bpy.utils.log.LogHandler())
log.setLevel(logging.INFO) # default is WARNING

# ----
import bpy
import logging

log = bpy.utils.log.getLogger("bpy.my_addon")  # automatically add handler (can also set log level based on blener's log level)
log.setLevel(logging.INFO)