Server-Side Validation


Refer to the lesson notes for Forms in Flask if you need reminders on basic set up steps for creating Flask forms.

In this lesson we'll create a form where a user can enter a time in hours and minutes, and then we'll validate the input and tell the user whether that is a valid time.

The steps we'll follow to accomplish this are:

  1. Create an HTML form with placeholders that will be filled with values using str.format and create a route for it
  2. Write the code to process the form and provide feedback to the user:
    1. Get the data from the request
    2. Provide error message to the user if input is invalid or provide success message if the input is valid:
      • Use a Try/Except block to test the input for whether it consists of integers
      • Provide unique error messages based on how the input was invalid (not an integer vs. out of range)
      • Create a message to display if input is valid (if the error messages are empty)
      • Leave valid values in place in the input fields, but remove invalid values


View the final code from this lesson.