Validate upload by csv only

Question

I have a small form where I ask the user to insert a csv file, however if the user inserts a file with different format he simply lets it pass. I’ve tried everything, but I’m not getting it done. Follow the code below:

Filing cabinet forms.py:

from django.forms import forms
from django import forms
from parte1.models import PresencaProf
from parte1.models import PresencaAula


class UploadArquivo(forms.ModelForm):


    class Meta:
        model = PresencaProf
        fields = ('evento', 'data', 'upload_csv',)


        def __init__(self, *args, **kwargs):
            super(UploadArquivo, self).__init__(*args, **kwargs)
            for visible in self.visible_fields():
                visible.field.widget.attrs['class'] = 'form-control'

        # Funcao para validar extensao csv
        def valida_csv_extensao(value):
            if not value.formulario.endswith('.csv'):
                raise forms.ValidationError("Erro!\nApenas arquivos .csv !")

            

        def clean(self):
            data = super(UploadArquivo, self).clean()

Filing cabinet views.py:

def presenca(request):

    lista = list()
    form = UploadArquivo()

    if request.method == 'POST':

        formulario = UploadArquivo(request.POST, request.FILES)
        data_evento ='-'.join(formulario.data['data'].split('/')[::-1])

        if formulario.is_valid():

            formulario.save(commit=False)
            formulario.save()

            arquivo = str(request.FILES.getlist('upload_csv')[0])

        f = open('csv/'+arquivo.replace(' ','_'), 'r')
        for line in f:
            line = line.split(',')

            participante = Professor.objects.filter(email_professor=line[1])
            if participante:
                verifica = PresencaAula.objects.filter(fk_professor__email_professor=line[1], data_aula=data_evento)
                if not verifica:
                    presenca = PresencaAula(fk_professor=participante[0], data_aula=data_evento).save()

            # print(line[1])
            if line[1]=="":
                lista.append(line[0] + ' <strong style="color: #FF0000">| Email não encontrado</strong>')
            else:
                lista.append(line[1])

        f.close()


    return render(request, 'upload.html', locals())

My last attempt was to create a function using the .endswith, but he’s shooting a mistake:

(...) line 34, in presenca
    participante = Professor.objects.filter(email_professor=line[1])
IndexError: list index out of range

I really appreciate it if someone can help me!!!