Exercise 12-09:
Write a program that validates user data entry. Try to find a valid ISBN or ISSN, as defined in previous exercises. Display a message stating whether the number is a valid ISBN or ISSN (identify which one in your response).
Answer:
##############################################################################
# Python From Scratch
# Author: Nilo Ney Coutinho Menezes
# Editora Novatec (c) 2010-2025 - LogiKraft 2025
# Site: https://pythonfromscratch.com
# ISBN: 978-85-7522-949-1 (Paperback), 978-85-7522-950-7 (hardcover), 978-85-7522-951-4 (ebook)
#
# File: chapter 12/exercise-12-09.py.py
##############################################################################
# Functions number, sequence and check pattern from listing 12.5
# Function cpf from exercise 12.07
# Function cnpj from exercise 12.08
import re
CPF_RE = r"^\d{3}\.\d{3}\.\d{3}-\d{2}$"
CNPJ_RE = r"^\d{2}\.\d{3}\.\d{3}/\d{4}-\d{2}$"
def cpf(input):
return bool(re.match(CPF_RE, input))
# Checks if input is a valid CNPJ, that is:
# A sequence in the format 99.999.999/9999-99
def cnpj(input):
return bool(re.match(CNPJ_RE, input))
inputs = [
"12.345.678/9012-34", # Valid CNPJ
"12.345.678-9012-34", # Invalid
"99.999.999/9999-99", # Valid CNPJ
"123.456.789-01", # Valid CPF
"23.456.789-01", # Invalid
"999.456.789-01", # Valid CPF
]
for input in inputs:
print(
f"{input}:\nis it a CNPJ? {'Yes' if cnpj(input) else 'No'}\nis it a CPF? {'Yes' if cpf(input) else 'No'}\n"
)