catch input type error

[mcmxl22]

I am trying to get this script to only accept integers.

number = int(input("Enter a number. "))
if isinstance(number, str):
    print("Entry must be a number")

I have also tried:

if type(number) is str:
    print("Entry must be a number")

I enter a and keep getting:

Error:
ValueError: invalid literal for int() with base 10: 'a'

Why dosen't this catch the error?