Django (audio) File Validation

I'm experimenting with a site that will allow users to upload audio files. I've read every doc that I can get my hands on but can't find much about validating files.

Total newb here (never done any file validation of any kind before) and trying to figure this out. Can someone hold my hand and tell me what I need to know?

As always, thank you in advance.

You want to validate the file before it gets written to disk. When you upload a file, the form gets validated then the uploaded file gets passed to a handler/method that deals with the actual writing to the disk on your server. So in between these two operations, you want to perform some custom validation to make sure it's a valid audio file

You could:

check if the the file is less then a certain size (good practice)
then check if the submitted file has a certain content type (i.e. an audio file)
- this is pretty useless as someone could easily spoof it
then check that the file ends in a certain extension (or extensions)
- this is also pretty useless
try read the file and see if it's actually audio

(I haven't tested this code)

models.py

class UserSong(models.Model):
    title = models.CharField(max_length=100)
    audio_file = models.FileField()

forms.py

class UserSongForm(forms.ModelForm):
     # Add some custom validation to our file field
     def clean_audio_file(self):
         file = self.cleaned_data.get('audio_file',False):
         if file:
             if file._size > 4*1024*1024:
                   raise ValidationError("Audio file too large ( > 4mb )")
             if not file.content-type in ["audio/mpeg","audio/..."]:
                   raise ValidationError("Content-Type is not mpeg")
             if not os.path.splitext(file.name)[1] in [".mp3",".wav" ...]:
                   raise ValidationError("Doesn't have proper extension")
             # Here we need to now to read the file and see if it's actually 
             # a valid audio file. I don't know what the best library is to 
             # to do this
             if not some_lib.is_audio(file.content):
                   raise ValidationError("Not a valid audio file")
             return file
         else:
             raise ValidationError("Couldn't read uploaded file")

views.py from utils import handle_uploaded_file

def upload_file(request):
    if request.method == 'POST':
        form = UserSongForm(request.POST, request.FILES)
        if form.is_valid():
            # If we are here, the above file validation has completed
            # so we can now write the file to disk
            handle_uploaded_file(request.FILES['file'])
            return HttpResponseRedirect('/success/url/')
    else:
        form = UploadFileForm()
    return render_to_response('upload.html', {'form': form})

utils.py

# from django's docs
def handle_uploaded_file(f):
    ext = os.path.splitext(f.name)[1]
    destination = open('some/file/name%s'%(ext), 'wb+')
    for chunk in f.chunks():
        destination.write(chunk)
    destination.close()

https://docs.djangoproject.com/en/dev/topics/http/file-uploads/#file-uploads https://docs.djangoproject.com/en/dev/ref/forms/fields/#filefield https://docs.djangoproject.com/en/dev/ref/files/file/#django.core.files.File