The “they” that you would have to contact is the community maintainers of Langchain.
Here is the API method being employed for CSV reading:
https://python.langchain.com/api_reference/community/document_loaders/langchain_community.document_loaders.csv_loader.CSVLoader.html
And the source:
https://python.langchain.com/api_reference/_modules/langchain_community/document_loaders/csv_loader.html#CSVLoader
If you want to tear into the langchain code to see what will work more universally, or report the improvement needed such as on ASCII + multi-byte UTF-8 CSV, (the source of the character error when cp1252 encoding is attempted), here is a cheap and easy bot text dump (which can only come about by extensive information and role prompting first).
The issue lies in the inability of the CSVLoader to handle files with unknown or unsupported encodings gracefully, even though it attempts to handle this with the autodetect_encoding option. The error originates because the loader defaults to a specific encoding (cp1255 in this case), which isn’t suitable for the given file, and it fails to retry with other encodings effectively.
Here’s a step-by-step solution to patch this issue, ensuring a robust way to handle various file encodings:
Proposed Fix: Enhancing Encoding Detection in CSVLoader
This fix will modify the CSVLoader class to improve how it detects and falls back to alternative encodings. It also ensures that even files with entirely unknown encodings are handled gracefully, e.g., by using utf-8 as a default fallback.
Implementation
Here is the patch code for the CSVLoader class, which can be directly used by users or submitted as a pull request to the LangChain repository:
import csv
from io import TextIOWrapper
from pathlib import Path
from typing import Iterator, Optional, Sequence, Union, Dict
from langchain_core.documents import Document
from langchain_community.document_loaders.base import BaseLoader
from langchain_community.document_loaders.helpers import detect_file_encodings
class PatchedCSVLoader(BaseLoader):
"""
Patched version of CSVLoader with improved encoding detection and fallback mechanism.
"""
def __init__(
self,
file_path: Union[str, Path],
source_column: Optional[str] = None,
metadata_columns: Sequence[str] = (),
csv_args: Optional[Dict] = None,
encoding: Optional[str] = None,
autodetect_encoding: bool = True, # Default to True for better compatibility
*,
content_columns: Sequence[str] = (),
):
"""
Args:
file_path: The path to the CSV file.
source_column: The name of the column in the CSV file to use as the source.
Optional. Defaults to None.
metadata_columns: A sequence of column names to use as metadata. Optional.
csv_args: A dictionary of arguments to pass to the csv.DictReader. Optional.
encoding: The encoding of the CSV file. Optional. Defaults to None.
autodetect_encoding: Whether to try to autodetect the file encoding.
content_columns: A sequence of column names to use for the document content.
"""
self.file_path = file_path
self.source_column = source_column
self.metadata_columns = metadata_columns
self.encoding = encoding
self.csv_args = csv_args or {}
self.autodetect_encoding = autodetect_encoding
self.content_columns = content_columns
def lazy_load(self) -> Iterator[Document]:
"""
Load the CSV file row by row with improved encoding handling.
"""
try:
yield from self._load_with_encoding(self.encoding)
except UnicodeDecodeError as e:
if self.autodetect_encoding:
detected_encodings = detect_file_encodings(self.file_path)
for encoding in detected_encodings:
try:
yield from self._load_with_encoding(encoding.encoding)
return
except UnicodeDecodeError:
continue
# Fallback to utf-8-sig if no detected encodings work
try:
yield from self._load_with_encoding("utf-8-sig")
return
except UnicodeDecodeError:
pass
raise RuntimeError(
f"Error loading {self.file_path}. Failed to decode with all attempted encodings."
) from e
except Exception as e:
raise RuntimeError(f"Error loading {self.file_path}") from e
def _load_with_encoding(self, encoding: Optional[str]) -> Iterator[Document]:
"""
Helper method to load the CSV file with a specific encoding.
"""
with open(self.file_path, newline="", encoding=encoding) as csvfile:
yield from self.__read_file(csvfile)
def __read_file(self, csvfile: TextIOWrapper) -> Iterator[Document]:
"""
Process the CSV file row by row and yield Documents.
"""
csv_reader = csv.DictReader(csvfile, **self.csv_args)
for i, row in enumerate(csv_reader):
try:
source = (
row[self.source_column]
if self.source_column is not None
else str(self.file_path)
)
except KeyError:
raise ValueError(
f"Source column '{self.source_column}' not found in CSV file."
)
content = "\n".join(
f"{k.strip() if k is not None else k}: {v.strip() if isinstance(v, str) else v}"
for k, v in row.items()
if (
k in self.content_columns
if self.content_columns
else k not in self.metadata_columns
)
)
metadata = {"source": source, "row": i}
for col in self.metadata_columns:
try:
metadata[col] = row[col]
except KeyError:
raise ValueError(
f"Metadata column '{col}' not found in CSV file."
)
yield Document(page_content=content, metadata=metadata)
How This Fix Works
-
Encoding Detection:
- The
autodetect_encoding option triggers the detect_file_encodings helper to identify possible encodings.
- It iterates through the detected encodings and retries opening the file until one succeeds.
-
Fallback Mechanism:
- If no detected encoding works, the patch attempts to decode the file using
utf-8-sig as a final fallback.
- This accounts for common issues like Byte Order Mark (BOM) in UTF-8 files.
-
Error Handling:
- If all encoding attempts fail, the loader raises a detailed
RuntimeError, helping users understand the failure.
-
Backward Compatibility:
- Existing arguments (
source_column, metadata_columns, etc.) are preserved to ensure compatibility with current usage.
How to Use
Standalone Usage
Replace the original CSVLoader with the PatchedCSVLoader in your code:
from your_module import PatchedCSVLoader
loader = PatchedCSVLoader(
file_path="./data.csv",
autodetect_encoding=True,
)
docs = loader.load()
Patch as a Pull Request
Include the PatchedCSVLoader class in your pull request to LangChain. Add this as a drop-in replacement for the existing CSVLoader, ensuring backward compatibility and resolving encoding issues.
Testing the Fix
-
Test Files:
- UTF-8 encoded file.
- File with BOM (e.g.,
utf-8-sig).
- Non-UTF encodings (e.g.,
cp1252, iso-8859-1).
- Corrupted or unsupported encoding files.
-
Expected Results:
- Files should load correctly for supported encodings.
- For unsupported or corrupted files, an appropriate error should be raised.
This fix not only resolves your immediate issue but also improves the library’s robustness, making it more reliable for the community.
Note that the new method has a new name - you’d have to overwrite the existing class name and test it for versatility on all types of CSV one might attempt, or expand the methods available.
