Improve error messages formatting in doc loaders (#4586)

# Cosmetic in errors formatting

Added appropriate spacing to the `ImportError` message in a bunch of
document loaders to enhance trace readability (including Google Drive,
Youtube, Confluence and others). This change ensures that the error
messages are not displayed as a single line block, and that the `pip
install xyz` commands can be copied to clipboard from terminal easily.

## Who can review?

@eyurtsev

langchain/document_loaders/image_captions.py

@@ -40,8 +40,8 @@ class ImageCaptionLoader(BaseLoader):
             from transformers import BlipForConditionalGeneration, BlipProcessor
         except ImportError:
             raise ValueError(
-                "transformers package not found, please install with"
-                "`pip install transformers`"
+                "`transformers` package not found, please install with "
+                "`pip install transformers`."
             )
 
         processor = BlipProcessor.from_pretrained(self.blip_processor)
@@ -67,7 +67,7 @@ class ImageCaptionLoader(BaseLoader):
             from PIL import Image
         except ImportError:
             raise ValueError(
-                "PIL package not found, please install with `pip install pillow`"
+                "`PIL` package not found, please install with `pip install pillow`"
             )
 
         try:

langchain/document_loaders/pdf.py

@@ -194,7 +194,7 @@ class PDFMinerLoader(BasePDFLoader):
             from pdfminer.high_level import extract_text  # noqa:F401
         except ImportError:
             raise ValueError(
-                "pdfminer package not found, please install it with "
+                "`pdfminer` package not found, please install it with "
                 "`pip install pdfminer.six`"
             )
 
@@ -222,7 +222,7 @@ class PDFMinerPDFasHTMLLoader(BasePDFLoader):
             from pdfminer.high_level import extract_text_to_fp  # noqa:F401
         except ImportError:
             raise ValueError(
-                "pdfminer package not found, please install it with "
+                "`pdfminer` package not found, please install it with "
                 "`pip install pdfminer.six`"
             )
 
@@ -256,7 +256,7 @@ class PyMuPDFLoader(BasePDFLoader):
             import fitz  # noqa:F401
         except ImportError:
             raise ValueError(
-                "PyMuPDF package not found, please install it with "
+                "`PyMuPDF` package not found, please install it with "
                 "`pip install pymupdf`"
             )
 

langchain/document_loaders/s3_file.py

@@ -22,7 +22,7 @@ class S3FileLoader(BaseLoader):
             import boto3
         except ImportError:
             raise ValueError(
-                "Could not import boto3 python package. "
+                "Could not import `boto3` python package. "
                 "Please install it with `pip install boto3`."
             )
         s3 = boto3.client("s3")