Add CSVLoader document loader (#1573)

Simple CSV document loader which wraps `csv` reader, and preps the file
with a single `Document` per row.

The column header is prepended to each value for context which is useful
for context with embedding and semantic search

docs/modules/document_loaders/examples/example_data/mlb_teams_2012.csv

@@ -0,0 +1,32 @@
+"Team", "Payroll (millions)", "Wins"
+"Nationals",     81.34, 98
+"Reds",          82.20, 97
+"Yankees",      197.96, 95
+"Giants",       117.62, 94
+"Braves",        83.31, 94
+"Athletics",     55.37, 94
+"Rangers",      120.51, 93
+"Orioles",       81.43, 93
+"Rays",          64.17, 90
+"Angels",       154.49, 89
+"Tigers",       132.30, 88
+"Cardinals",    110.30, 88
+"Dodgers",       95.14, 86
+"White Sox",     96.92, 85
+"Brewers",       97.65, 83
+"Phillies",     174.54, 81
+"Diamondbacks",  74.28, 81
+"Pirates",       63.43, 79
+"Padres",        55.24, 76
+"Mariners",      81.97, 75
+"Mets",          93.35, 74
+"Blue Jays",     75.48, 73
+"Royals",        60.91, 72
+"Marlins",      118.07, 69
+"Red Sox",      173.18, 69
+"Indians",       78.43, 68
+"Twins",         94.08, 66
+"Rockies",       78.06, 64
+"Cubs",          88.19, 61
+"Astros",        60.65, 55
+

langchain/document_loaders/__init__.py

@@ -4,6 +4,7 @@ from langchain.document_loaders.airbyte_json import AirbyteJSONLoader
 from langchain.document_loaders.azlyrics import AZLyricsLoader
 from langchain.document_loaders.college_confidential import CollegeConfidentialLoader
 from langchain.document_loaders.conllu import CoNLLULoader
+from langchain.document_loaders.csv import CSVLoader
 from langchain.document_loaders.directory import DirectoryLoader
 from langchain.document_loaders.docx import UnstructuredDocxLoader
 from langchain.document_loaders.email import UnstructuredEmailLoader
@@ -96,4 +97,5 @@ __all__ = [
     "CoNLLULoader",
     "GoogleApiYoutubeLoader",
     "GoogleApiClient",
+    "CSVLoader",
 ]

langchain/document_loaders/csv.py

@@ -0,0 +1,47 @@
+from csv import DictReader
+from typing import Dict, List, Optional
+
+from langchain.docstore.document import Document
+from langchain.document_loaders.base import BaseLoader
+
+
+class CSVLoader(BaseLoader):
+    """Loads a CSV file into a list of documents.
+
+    Each document represents one row of the CSV file. Every row is converted into a
+    key/value pair and outputted to a new line in the document's page_content.
+
+    Output Example:
+        .. code-block:: txt
+
+            column1: value1
+            column2: value2
+            column3: value3
+    """
+
+    def __init__(self, file_path: str, csv_args: Optional[Dict] = None):
+        self.file_path = file_path
+        if csv_args is None:
+            self.csv_args = {
+                "delimiter": ",",
+                "quotechar": '"',
+            }
+        else:
+            self.csv_args = csv_args
+
+    def load(self) -> List[Document]:
+        docs = []
+
+        with open(self.file_path, newline="") as csvfile:
+            csv = DictReader(csvfile, **self.csv_args)  # type: ignore
+            for row in csv:
+                docs.append(
+                    Document(
+                        page_content="\n".join(
+                            f"{k.strip()}: {v.strip()}" for k, v in row.items()
+                        ),
+                        metadata={"source": self.file_path},
+                    )
+                )
+
+        return docs