Allow pathlib.Path to be passed to all engines (#4701)

* Allow pathlib.Path to be used in open_dataset

* Fix mypy run. It doesn't like isinstance with os.PathLike

* Add patlib.Path support to netCDF4

* Sympler code

* Move os.fspath down the call tree

Author: alexamici

xarray/backends/netCDF4_.py

@@ -1,5 +1,7 @@
 import functools
 import operator
+import os
+import pathlib
 from contextlib import suppress
 
 import numpy as np
@@ -335,6 +337,9 @@ def open(
     ):
         import netCDF4
 
+        if isinstance(filename, pathlib.Path):
+            filename = os.fspath(filename)
+
         if not isinstance(filename, str):
             raise ValueError(
                 "can only read bytes or file-like objects "

xarray/backends/zarr.py

@@ -1,3 +1,6 @@
+import os
+import pathlib
+
 import numpy as np
 
 from .. import coding, conventions
@@ -284,6 +287,10 @@ def open_group(
     ):
         import zarr
 
+        # zarr doesn't support pathlib.Path objects yet. zarr-python#601
+        if isinstance(store, pathlib.Path):
+            store = os.fspath(store)
+
         open_kwargs = dict(mode=mode, synchronizer=synchronizer, path=group)
         if chunk_store:
             open_kwargs["chunk_store"] = chunk_store