CODEWITHSUNDEEP
pythonazureazure-functionsexport-to-csvazure-blob-storage
Lawton
Lawton

Reputation: 143

How to write to azure output blob with python csv writer?

I am trying to read in an excel file from blob storage using an azure function, and output a csv file. I have successfully read in the excel file with openpyxl and processed it, but I am having trouble with writing to the output blob. I am not very familiar with python streams. In my original code I was opening a local file, but now I am trying to open a stream and write to it and then save that stream to the output blob. My function.json looks like

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "name": "myblob",
      "type": "blobTrigger",
      "direction": "in",
      "path": "example/{name}.xlsx",
      "connection": "AzureWebJobsStorage"
    },
    {
      "name": "outputblob",
      "type": "blob",
      "path": "example/processed-csv.csv",
      "connection": "AzureWebJobsStorage",
      "direction": "out"
    }
  ]
}

My code looks like

logging.info(f"Python blob trigger function processed blob \n"
                 f"Name: {myblob.name}\n"
                 f"Blob Size: {myblob.length} bytes")
    print('loading workbook')
    filename = myblob.name
    wb = openpyxl.load_workbook(filename = BytesIO(myblob.read()))
    logging.info(f"Loaded workbook \n")
### Excel processing here
    logging.info(f"writing csv \n")
        with StringIO() as f:
            c = csv.writer(f)
            for r in coreWorksheet.rows:
                c.writerow([cell.value for cell in r])
            outputblob.set(f)

I am getting an error message of ValueError: I/O operation on closed file with this code, though I have attempted to write to the output blob in a couple different ways.

Upvotes: 0

Views: 2724

Answers (2)

Aadithyue Nair
Aadithyue Nair

Reputation: 11

"ValueError: I/O operation on closed file", this error occurs when you are attempting to write into the blob storage but the IO stream returns an object.

You need to use outputblob.set(f.getvalue()) to get the value and write to the blob.

If you are attempting to copy the csv file into a database, output binding doesn't seem to be the best option since the csv file is written only after the function execution and not while setting it as mentioned above. In this case, you can opt to use the azure-storage-blob python package. For more details

Upvotes: 1

Frank Borzage
Frank Borzage

Reputation: 6816

You need to use outputblob.set(f.getvalue()).

Please refer to the following code:

import logging
import openpyxl
import azure.functions as func
import io
import csv


def main(myblob: func.InputStream, outputblob: func.Out[func.InputStream]):
    logging.info(f"Python blob trigger function processed blob \n"
                 f"Name: {myblob.name}\n"
                 f"Blob Size: {myblob.length} bytes")
    logging.info('loading workbook')
    wb = openpyxl.load_workbook(filename = io.BytesIO(myblob.read()))
    coreWorksheet = wb['testSheet1']
    logging.info(coreWorksheet)
    ### Excel processing here
    logging.info(f"writing csv \n")
    with io.StringIO() as f:
        c = csv.writer(f)
        for r in coreWorksheet.rows:
            c.writerow([cell.value for cell in r])
        outputblob.set(f.getvalue())

Upvotes: 2

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