Make PreProcessor.process() work on lists of documents (#1163)

* Add process_batch method

* Rename methods

* Fix doc string, satisfy mypy

* Fix mypy CI

* Fix typp

* Update tutorial

* Fix argument name

* Change arg name

* Incorporate reviewer feedback

haystack/preprocessor/base.py

@@ -1,4 +1,4 @@
-from typing import List, Dict, Any, Optional
+from typing import List, Dict, Any, Optional, Union
 
 from haystack import BaseComponent
 
@@ -8,7 +8,7 @@ class BasePreProcessor(BaseComponent):
 
     def process(
         self,
-        document: dict,
+        documents: Union[dict, List[dict]],
         clean_whitespace: Optional[bool] = True,
         clean_header_footer: Optional[bool] = False,
         clean_empty_lines: Optional[bool] = True,
@@ -50,7 +50,7 @@ class BasePreProcessor(BaseComponent):
         **kwargs,
     ):
         documents = self.process(
-            document=document,
+            documents=document,
             clean_whitespace=clean_whitespace,
             clean_header_footer=clean_header_footer,
             clean_empty_lines=clean_empty_lines,

haystack/preprocessor/preprocessor.py

@@ -3,7 +3,7 @@ import re
 from copy import deepcopy
 from functools import partial, reduce
 from itertools import chain
-from typing import List, Optional, Generator, Set
+from typing import List, Optional, Generator, Set, Union
 
 import nltk
 from more_itertools import windowed
@@ -92,7 +92,7 @@ class PreProcessor(BasePreProcessor):
 
     def process(
         self,
-        document: dict,
+        documents: Union[dict, List[dict]],
         clean_whitespace: Optional[bool] = None,
         clean_header_footer: Optional[bool] = None,
         clean_empty_lines: Optional[bool] = None,
@@ -101,9 +101,51 @@ class PreProcessor(BasePreProcessor):
         split_overlap: Optional[int] = None,
         split_respect_sentence_boundary: Optional[bool] = None,
     ) -> List[dict]:
+
         """
-        Perform document cleaning and splitting. Takes a single document as input and returns a list of documents.
+        Perform document cleaning and splitting. Can take a single document or a list of documents as input and returns a list of documents.
         """
+
+        kwargs = {
+            "clean_whitespace": clean_whitespace,
+            "clean_header_footer": clean_header_footer,
+            "clean_empty_lines": clean_empty_lines,
+            "split_by": split_by,
+            "split_length": split_length,
+            "split_overlap": split_overlap,
+            "split_respect_sentence_boundary": split_respect_sentence_boundary
+        }
+
+        ret = []
+
+        if type(documents) == dict:
+            ret = self._process_single(
+                document=documents,
+                **kwargs                #type: ignore
+        )
+        elif type(documents) == list:
+            ret = self._process_batch(
+                documents=list(documents),
+                **kwargs
+            )
+
+        else:
+            raise Exception("documents provided to PreProcessor.prepreprocess() is not of type list nor Document")
+
+        return ret
+
+    def _process_single(
+        self,
+        document,
+        clean_whitespace: Optional[bool] = None,
+        clean_header_footer: Optional[bool] = None,
+        clean_empty_lines: Optional[bool] = None,
+        split_by: Optional[str] = None,
+        split_length: Optional[int] = None,
+        split_overlap: Optional[int] = None,
+        split_respect_sentence_boundary: Optional[bool] = None,
+    ) -> List[dict]:
+
         if clean_whitespace is None:
             clean_whitespace = self.clean_whitespace
         if clean_header_footer is None:
@@ -134,6 +176,14 @@ class PreProcessor(BasePreProcessor):
         )
         return split_documents
 
+    def _process_batch(
+        self,
+        documents: List[dict],
+        **kwargs
+    ) -> List[dict]:
+        nested_docs = [self.process(d, **kwargs) for d in documents]
+        return [d for x in nested_docs for d in x]
+
     def clean(
         self,
         document: dict,

tutorials/Tutorial8_Preprocessing.ipynb

@@ -455,8 +455,7 @@
     "    split_length=100,\n",
     "    split_respect_sentence_boundary=True\n",
     ")\n",
-    "nested_docs = [preprocessor.process(d) for d in all_docs]\n",
+    "docs = preprocessor.process(all_docs)\n",
-    "docs = [d for x in nested_docs for d in x]\n",
     "\n",
     "print(f\"n_files_input: {len(all_docs)}\\nn_docs_output: {len(docs)}\")"
    ],