In python, how to check if a date is valid?

I am building a kind of calender web app

I have set up the following form in HTML

<form action='/event' method='post'>
Year ("yyyy"):  <input type='text' name='year' />
Month ("mm"):  <input type='text' name='month' />
Day ("dd"):  <input type='text' name='day' />
Hour ("hh"):  <input type='text' name='hour' />
Description:  <input type='text' name='info' />
             <input type='submit' name='submit' value='Submit'/>
</form>

The input from the user is then submited in the a cherrypy server

I am wondering, is there a way to check if the date entered by the user is a valid date?

Obviously I could write a whole lot of if statements, but are there any built in function that can check this?

Thanks