title: Validating StringField based on input in a separate Field on WTForms
body: <p>i am working on a Form whereby a user can manage the inventory of a business. Specifically, i want to be able to add a certain amount of stock in a StringField, while in a separate StringField - be able to add in the amount of sales not exceeding the amount of stock added. </p>
  
  <p>I would also like to know if it would be possible to make users input numbers only in the fields. I have tried using IntegerField but it ends up with a Name Error stating that IntegerField is not recognised.</p>
  
  <pre><code>from wtforms import Form, StringField, RadioField, SelectField, TextAreaField, validators
  class CreateGPUForm(Form):
      GPUBrand = SelectField('GPU Brand',default='NVIDIA' ,choices=[('NVIDIA', 'NVIDIA'),('MSI/Micro Star International', 'MSI/Micro Star International'),('Zotac', 'Zotac'),('EVGA', 'EVGA'),('Galax', 'Galax'),('Power Color', 'Power Color'),('Sapphire', 'Sapphire')], render_kw={'readonly': False})
      GPUName = StringField('GPU Name/Series', [validators.Length(min=1), validators.DataRequired()], render_kw={'readonly': False})
      GPUStock = IntegerField('Enter GPU Stock To Add', [validators.Length(min=1), validators.DataRequired()])
      GPUUnitPrice = StringField('GPU Manufacturing Price', [validators.Length(min=1), validators.DataRequired()], render_kw={'readonly': False})
      GPUSalePrice = StringField('GPU Retail Price', [validators.Length(min=1), validators.DataRequired()], render_kw={'readonly': False})
      GPUSales = StringField('Amount of GPUs Sold', [validators.Length(min=1), validators.DataRequired()], render_kw={'readonly': False})
  </code></pre>