How can I read a number as input from the user?

Answer:

Use the built-in input() function to read input from the user. (If you are using Python 2, use raw_input() instead.) These functions return a string, so you will have to cast the returned value to an integer with the built-in int() function. If the user entered an invalid number, this will raise a ValueError that you can catch. Here is an example:

string_input = input("Enter a number: ")
try:
    number = int(string_input)
    print(number)

except ValueError:
    print("That was no number!")

And here's the result of running it:

$ python3 int.py
Enter a number: 88
88
$ python3 int.py
Enter a number: asdf
That was no number!

You can embed the whole thing in a while loop and break out only once a valid number was entered.