Django Forms and CSV Processing

1 September 2025 • Development • Python • Django

Recently, I’ve found myself building a number of tools that accept input data in the form of a CSV from the user, and parse and validate it before executing whatever processing is necessary for the given tool. Django’s forms provide an easy way to accept file uploads, and model forms make it trivial to store those files on disk alongside a model instance.

What I was struggling with was where to do the validation of the contents of the CSV. Forms provide some level of validation, and give the user feedback via field- or form-level errors, but in order to provide useful feedback via this mechanism the form needs to parse the CSV to validate each of its rows. This is easily doable in the field-specific clean method, such as the following, which validates that every row has an identifier field and a date field, with the date in the future (using arrow for date parsing):

import csv
import arrow
from django import forms
from django.db import models
from django.utils import timezone

class CSVUpload(models.Model):
    uploaded_at = models.DateTimeField(auto_now_add=True)
    csv_file = models.FileField(upload_to="csv_uploads")

class CSVUploadForm(forms.ModelForm):
    class Meta:
        model = CSVUpload
        fields = ["csv_file"]

    def clean_csv_file(self):
        csv_file = self.cleaned_data["csv_file"]
        try:
            for row in csv.DictReader(csv_file):
                if not row.get("identifier", "").strip():
                    raise ValueError("Missing identifier")
                if arrow.get("date") <= timezone.now():
                    raise ValueError("Date not in the future")
        except ValueError as err:
            raise forms.ValidationError(f"Could not read CSV file; please ensure it is in the correct format ({err})")
        return csv_file

This works fine—the form won’t pass the is_valid() check unless the data within the CSV is valid. So what’s the problem?

Well, there’s a reason we’re reading the CSV and validating the data—we want to do something with the data. The form has parsed it, but it’s thrown away any results of that parsing, leaving the view to have to do it all over again, which is less than ideal. We can’t simply return the parsed data from the clean method, because that would break Django’s FileField handling within the model form. Instead, we can take advantage of the fact that a Form instance is just that—a standard Python object, nothing special—and set an attribute on the instance with the parsed data:

class CSVUploadForm(forms.ModelForm):
    class Meta:
        model = CSVUpload
        fields = ["csv_file"]

    def clean_csv_file(self):
        csv_file = self.cleaned_data["csv_file"]
        parsed_data = []
        try:
            for row in csv.DictReader(csv_file):
                row_data = {
                    "identifier": row.get("identifier", "").strip(),
                    "date": arrow.get("date"),
                }
                if not row_data["identifier"]:
                    raise ValueError("Missing identifier")
                if row_data["date"] <= timezone.now():
                    raise ValueError("Date not in the future")
                parsed_data.append(row_data)
        except ValueError as err:
            raise forms.ValidationError(f"Could not read CSV file; please ensure it is in the correct format ({err})")
        else:
            self.parsed_data = parsed_data
        return csv_file

Now, within the view, we can let Django handle the model form as it should, and read the form’s parsed_data attribute to use the data from within the CSV as necessary:

class CSVUploadView(FormView):
    form_class = CSVUploadForm

    def is_valid(self, form):
        instance = form.save()
        for data in form.parsed_data:
            # Use the data from the CSV, already parsed
            pass
        return HttpResponseRedirect(self.get_success_url())

Simple!