Thanks for the bug report!

shutil.move should certainly accept a path object, as shutil.copy does, though it should be noted that in your example, 'path' could become out of date as it does not refresh the path information. For example, with shutil.move fixed:

    >>> import os, pathlib, shutil
    >>> os.mkdir('test1')
    >>>
    >>> os.mkdir('test2')
    >>> path = pathlib.Path('test1')
    >>> path.absolute()
    PosixPath('/Users/e/Development/OSS/cpython/test1')
    >>> shutil.move(path, 'test2')
    'test2/test1'
    >>> path.absolute()
    PosixPath('/Users/e/Development/OSS/cpython/test2')

test1 is now actually at '/Users/e/Development/OSS/cpython/test2/test1'

For the fix:
I did a bit of digging and the error comes from a helper method _basename that uses rstrip to remove a trailing separator, hence the error as rstrip doesn't exist for a path object (and I don't think it makes sense that it should, though that was one solution). Removing the trailing separator is, however, very important in determining the full destination path.

After trying a few different approaches, I think the simplest way is to cast the src to a string before finding its appropriate basename. I also added some comments to make it more clear why _basename is used over os.path.basename to hopefully save someone else time in the future.

A more robust option would be to explicitly handle Path objects or to handle exceptions for any dst that cannot be cast to a string. However, the current patch fixes the issue without introducing new problems.

In my test, the second call to path.absolute() is just returning the same result as the first call, which is what I would expect (as you say, the path object doesn't update automatically).

However, your output shows it returning '/Users/e/Development/OSS/cpython/test2' instead of the (now broken) path from the first call. Maybe I'm missing something?

Ah, you're right. That was a typo when I was redacting my full path. The path object remains unchanged even though the directory has moved.

Should have been:

    >>> import os, pathlib, shutil
    >>> os.mkdir('test1')
    >>> os.mkdir('test2')
    >>> path = pathlib.Path('test1')
    >>> path.absolute()
    PosixPath('/Users/e/Development/OSS/cpython/test1')
    >>> shutil.move(path, 'test2')
    'test2/test1'
    >>> path.absolute()
    PosixPath('/Users/e/Development/OSS/cpython/test1')

test1 is now actually at '/Users/e/Development/OSS/cpython/test2/test1'

New changeset cf57cab by Miss Islington (bot) (Maxwell A McKinnon) in branch 'master':
bpo-32689: Updates shutil.move to allow for Path objects to be used as source arg (GH-15326)
cf57cab

3.9 only!