title: Allow fields to be valid or non-valid based on DateField ranges
body: <p>I have a model called products, see below:</p>
  <pre class="lang-py prettyprint-override"><code>class Product(models.Model):
  
      name = models.CharField(max_length=200, null=True)
      r_price = models.FloatField(null=True)
      d_price = models.FloatField(null=True, blank=True, default='')
      start_date = models.DateField(null=True, blank=True, default='')
      end_date = models.DateField(null=True, blank=True, default='')
  </code></pre>
  <p>The datefields that I have in my model is called start_date and end_date.</p>
  <p>My intention is that if the current date falls within the range of start_date and end_date, d_price will be valid (submitting values within its form).</p>
  <p>If the current date is not within the range of start_date and end_date or if the current date surpasses the end date, the r_price field will be valid into taking values to be submitted and d_price will no longer be valid.</p>
  <p>See below for views based on the model of when creating and updating instances.</p>
  <p>When creating instances -</p>
  <pre class="lang-py prettyprint-override"><code>def NewProductProfile(request):
      form = CreateProductForm()
      if request.method == 'POST':
          form = CreateProductForm(request.POST or None)
          if form.is_valid():
              form.save()
              return redirect('product_list')
      return render(request, 'accounts/new_product_profile.html', {'form': form})
  </code></pre>
  <p>When updating instances -</p>
  <pre class="lang-py prettyprint-override"><code>def EditProduct(request, pk):
  
      product = Product.objects.get(id=pk)
      form = ProductForm(instance=product)
      if request.method == 'POST':
          form = ProductForm(request.POST, instance=product)
          if form.is_valid():
              form.save()
              return redirect('product_list')
  
      return render(request, 'accounts/edit_product_profile.html', {'form': form})
  </code></pre>
  <p>Valid, meaning that the field mentioned will be activated.</p>
  <p>For example, if the current date falls in the range of start_date and end_date, when updating the instance when submitting the form.</p>
  <p>The Float value with in r_price will not be considered and not saved within the database when it is submitted within its form, rather it will only consider d_price(if the current date falls within the range of the start_date and end_date).</p>
  <p>Therefore if the current date is not in between the start_date and end_date, the float value in d_price will not be saved, but r_price will be saved within the database when updating instances of the product when submitting through the form.</p>
  <p>The start_date and end_date fields will be manual inputted by the intended user.</p>
  <p>How will this be implemented?</p>