Calls to Attributes of a Class

[SKarimi]

how does a direct call to openpyxl.load_workbook work?

According to OpenPyXL documentation, load_workbook is a submodule of a the subpackage reader i.e:
openpyxl.reader.excel.load_workbook

However a direct call to openpyxl.load_workbook works fine while using other submodules of openpyxl need the full callout. See below:

Initially in my code I had:

import openpyxl
try:
    openpyxl.load_workbook(filename)
except openpyxl.InvalidFileException as ife:
    print(ife)

which gave me the following error:

Error:
    except openpyxl.InvalidFileException as ife:
AttributeError: module 'openpyxl' has no attribute 'InvalidFileException'

however, when I changed line 4 to:

except openpyxl.utils.exceptions.InvalidFileException as ife:

exception handling work without an error.

Why full Callout required on one and not the other submodule? I could not find anything in the Documentation.