How to only allow certain characters in Tkinter Entry

Question

I am a beginner and started using Tkinter. I have 2 entries. For one I only want to allow a 3digit number, no spaces or anything. The other is only allow numbers and letters but limit it to 7 characters again no spaces. How could I do this. Thanks. I am using Python 2.7.

Answer 1

Here is the documentation describing one possible solution. Read it, try writing some code, and if it doesn't work, come back with the code and the errors/problems and we can help you.