adds copy-constructor to UPath

[normanrz]

Adds a new capability to the UPath constructor for copying UPath objects including their attached kwargs.

a = UPath("s3://bucket/folder", key="...", secret="...")
b = UPath(a)

assert b._kwargs["key"] == "..."

Fixes #49

[normanrz]

To further motivate this: Copying is also the behavior of the pathlib.Path constructor. A user can pass a valid argument in either a str, os.PathLike or pathlib.Path instance and a new Path instance will be created. This is handy for normalizing method arguments, like this:

def do_stuff(path: Union[str, os.PathLike, Path]) -> None:
    path = Path(path)
    assert isinstance(path, Path)
    ...

When UPath in its current form, we have to do the following (in order to not lose essential kwargs):

def do_stuff(path: Union[str, os.PathLike, Path, UPath]) -> None:
    path = make_upath(path)
    assert isinstance(path, UPath)
    ...

def make_upath(maybe_path: Union[str, PathLike, Path, UPath]) -> UPath:
    return maybe_path if isinstance(maybe_path, UPath) else UPath(maybe_path)

[jstriebel]

That's very useful IMO 👍 I added a few comments:

[jstriebel]

You might also rewrite args and kwargs and simply continue with the constructor, but also fine like this.

[jstriebel]

Shouldn't this also check for empty kwargs?

Suggested change

	if len(args) == 1 and isinstance(args[0], cls):
	if len(args) == 1 and isinstance(args[0], cls) and len(kwargs) == 0:

[andrewfulton9]

What if someone wants to do something like:

a = UPath("s3://bucket/folder", key="...", secret="...")
b = UPath(a, 'file')

I think checking if len(args) = 1 would make this not possible. Could we instead pop the first arg if its an instance of UPath and append the rest of args to new_args? I would also say allow kwargs to be set and do something like new_kwargs.update(kwargs).

[jstriebel]

You could directly use __reduce__ instead:

Suggested change

	new_args = (
	other._format_parsed_parts(
	other._drv, other._root, other._parts
	),
	)
	new_kwargs = {}
	if hasattr(other, "_kwargs"):
	new_kwargs = other._kwargs.copy()
	new_kwargs.pop("_url", None)
	_, new_args, new_kwargs = other.__reduce__()

[andrewfulton9]

This looks good to me. I'll go ahead and merge it. Thanks @normanrz!