Return Excel/CSV File as a Response Stream FastAPI

Code base to return excel/csv file using Streaming Response in FastAPI

Returning an excel file through Streaming Response

1. Writing data to an excel stream from dataframe

   from io import BytesIO

   stream = BytesIO()
df.to_excel(stream, index=False, engine="openpyxl") # Note: need to install openpyxl

2. Return a Streaming Response Object from FastAPI responses module

   ```
   from fastapi.responses import StreamingResponse

   response = StreamingResponse( iter([stream.getvalue()]), media_type="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", headers = { 'Content-Disposition': 'attachment;filename=sample_filename.xlsx',
   'Access-Control-Expose-Headers': 'Content-Disposition' #this is optional
   })
   return response
   ```

Returning an csv file through Streaming Response

1. Writing data to an csv stream from dataframe

   from io import StringIO

   stream = StringIO()
df.to_csv(stream, index=False)

2. Return a Streaming Response Object from FastAPI responses module

   ```
   from fastapi.responses import StreamingResponse

   response = StreamingResponse(
   iter([stream.getvalue()]), media_type="text/csv",
   headers={
   'Content-Disposition': 'attachment;filename=sample_filename.csv', 'Access-Control-Expose-Headers': 'Content-Disposition' # this is optional
   })
   return response ```