Error while validating User Input in Python - python-3.8

Question

I am having problem validating the user input (I am asking user if they wish to continue with the program of calculating factorial). The code is as follows: (User input validation is towards the end of the main function and I have not included the factorial function)
def main():
valid_inp = False
usr_continue = True
while usr_continue:
while valid_inp == False:
usr_inp = int(input('Please ENTER a number: '))
if usr_inp < 0:
print('ERROR, INVALID INPUT')
else:
valid_inp = True
continue
result = factorial(usr_inp)
print(str(result) + '\n')
con_inp = str(input('Would you like to continue ? '))
if con_inp == 'Y' or con_inp == 'y':
usr_continue
elif con_inp == 'N' or con_inp == 'n':
print('Goodbye...')
break
main()

Answer 1

Make a function that only returns on valid input. Use an exception handler to deal with bad integer input, then validate the integer is the range you want:
from math import factorial
def get_nonnegative_integer(prompt):
while True:
try:
val = int(input(prompt)) # bad input for int such as "abc" will raise ValueError
if val >= 0: # good input will be range-checked
return val
else:
print('enter a number >= 0')
except ValueError:
print('invalid input for integer')
def main():
while True:
usr_inp = get_nonnegative_integer('Please enter a number: ')
result = factorial(usr_inp)
print(result)
con_inp = input('Would you like to continue(Y/n)? ').upper() # default Yes
if con_inp.startswith('N'):
print('Goodbye...')
break
main()