How to use pathlib.Path.expanduser() and amend and use a PosixPath value?

Question

Below shows how I obtained user1's home directory, create a new sub-directory name and create a new sub-directory there via python 3.6's os module.

>>> import os.path
>>> import os
>>> a = os.path.expanduser('~')
>>> a
'/home/user1'
>>> a_sub_dir = a + '/Sub_Dir_1'
>>> a_sub_dir
'/home/user1/Sub_Dir_1'
>>> def create_sub_dir( sub_dir ):
    try:
        os.makedirs( sub_dir, mode=0o777, exist_ok=False )
    except FileExistsError:
        print('Sub_directory already exist, no action taken.')
    else:
        print('Created sub_directory.')
>>> create_sub_dir( a_sub_dir )
Created sub_directory.
>>> create_sub_dir( a_sub_dir )
Sub_directory already exist, no action taken.

I would like to achieve the same as above via python 3.6's pathlib module. However, I can't seem to get it to work (see below). My questions:

1. How do I use Path.expanduser()?
2. How do I amend the info in a PosixPath(......) since it is not a string so that I can reuse it?
3. I would like to amend the PosixPath and use it in my make_sub_dir() function. Will it work? Presently, I explicitly defined the new sub directory that i want to create to check that my make_sub_dir() function works.

Appreciate guidance on how to use pathlib. Thanks in advance.

>>> from pathlib import Path
>>> b = Path.expanduser('~')
Traceback (most recent call last):
  File "<pyshell#87>", line 1, in <module>
    b = Path.expanduser('~')
  File "/usr/lib/python3.6/pathlib.py", line 1438, in expanduser
    if (not (self._drv or self._root) and
AttributeError: 'str' object has no attribute '_drv'
>>> b = Path.expanduser('~/')
Traceback (most recent call last):
  File "<pyshell#88>", line 1, in <module>
    b = Path.expanduser('~/')
  File "/usr/lib/python3.6/pathlib.py", line 1438, in expanduser
    if (not (self._drv or self._root) and
AttributeError: 'str' object has no attribute '_drv'
>>> b = Path.home()
>>> b
PosixPath('/home/user1')
>>> b_sub_dir = b + '/Sub_Dir_1'
Traceback (most recent call last):
  File "<pyshell#91>", line 1, in <module>
    b_sub_dir = b + '/Sub_Dir_1'
TypeError: unsupported operand type(s) for +: 'PosixPath' and 'str'
>>> def make_sub_dir( sub_dir ):
    try:
        Path(sub_dir).mkdir(mode=0o777, parents=False, exist_ok=False)
    except FileNotFoundError:
        print('Parent directory do not exist, no action taken.')
    except FileExistsError:
        print('Sub_directory already exist, no action taken.')
    else:
        print('Created sub_directory.')
>>> make_sub_dir( '/home/user1/Sub_Dir_1' )
Sub_directory already exist, no action taken.
>>> make_sub_dir( '/home/user1/Sub_Dir_1' )
Created sub_directory.
>>> make_sub_dir( '/home/user1/Sub_Dir_1' )
Sub_directory already exist, no action taken.

Answer 1

pathlib's expanduser works differently than the one in os.path: it is applied to a Path object and takes no arguments. as shown in the doc you can either use:

>>> from pathlib import Path
>>> p = Path('~/films/Monty Python')
>>> p.expanduser()
PosixPath('/home/eric/films/Monty Python')

or work with .home():

>>> form pathlib import Path
>>> Path.home()
PosixPath('/home/antoine')

then in order to join directories you should use / (instead of +):

b_sub_dir = b / 'Sub_Dir_1'