community: better support of pathlib paths in document loaders (#18396)

So this arose from the
https://github.com/langchain-ai/langchain/pull/18397 problem of document
loaders not supporting `pathlib.Path`.

This pull request provides more uniform support for Path as an argument.
The core ideas for this upgrade: 
- if there is a local file path used as an argument, it should be
supported as `pathlib.Path`
- if there are some external calls that may or may not support Pathlib,
the argument is immidiately converted to `str`
- if there `self.file_path` is used in a way that it allows for it to
stay pathlib without conversion, is is only converted for the metadata.

Twitter handle: https://twitter.com/mwmajewsk

libs/community/langchain_community/document_loaders/unstructured.py

@@ -1,6 +1,7 @@
 """Loader that uses unstructured to load files."""
 import collections
 from abc import ABC, abstractmethod
+from pathlib import Path
 from typing import IO, Any, Callable, Dict, Iterator, List, Optional, Sequence, Union
 
 from langchain_core.documents import Document
@@ -155,7 +156,7 @@ class UnstructuredFileLoader(UnstructuredBaseLoader):
 
     def __init__(
         self,
-        file_path: Union[str, List[str]],
+        file_path: Union[str, List[str], Path, List[Path]],
         mode: str = "single",
         **unstructured_kwargs: Any,
     ):
@@ -169,9 +170,13 @@ class UnstructuredFileLoader(UnstructuredBaseLoader):
         if isinstance(self.file_path, list):
             elements = []
             for file in self.file_path:
+                if isinstance(file, Path):
+                    file = str(file)
                 elements.extend(partition(filename=file, **self.unstructured_kwargs))
             return elements
         else:
+            if isinstance(self.file_path, Path):
+                self.file_path = str(self.file_path)
             return partition(filename=self.file_path, **self.unstructured_kwargs)
 
     def _get_metadata(self) -> dict:
@@ -179,14 +184,16 @@ class UnstructuredFileLoader(UnstructuredBaseLoader):
 
 
 def get_elements_from_api(
-    file_path: Union[str, List[str], None] = None,
+    file_path: Union[str, List[str], Path, List[Path], None] = None,
     file: Union[IO, Sequence[IO], None] = None,
     api_url: str = "https://api.unstructured.io/general/v0/general",
     api_key: str = "",
     **unstructured_kwargs: Any,
 ) -> List:
     """Retrieve a list of elements from the `Unstructured API`."""
-    if isinstance(file, collections.abc.Sequence) or isinstance(file_path, list):
+    if is_list := isinstance(file_path, list):
+        file_path = [str(path) for path in file_path]
+    if isinstance(file, collections.abc.Sequence) or is_list:
         from unstructured.partition.api import partition_multiple_via_api
 
         _doc_elements = partition_multiple_via_api(
@@ -206,7 +213,7 @@ def get_elements_from_api(
         from unstructured.partition.api import partition_via_api
 
         return partition_via_api(
-            filename=file_path,
+            filename=str(file_path),
             file=file,
             api_key=api_key,
             api_url=api_url,