如何输入非数字来打印其他内容，而不是使用 while 循环出错？

Question

I have to calculate factorials of given numbers, which have inputs of 4, 9, and abc123. This is my coding so far but for abc123 is where the error is. How can I edit this so that it does not show an error but printing something else?

for i in range(0,2):
  num = int(input('Enter a number: '))
  factorial = 1
  if num < 0:
    print('Sorry! Factorials cannot be negative numbers.')
  else:
    for i in range(1, num + 1):
      factorial = factorial*i
    print(num, '!=', factorial)

Answer 1

You could use try except to handle non-integers as:

for i in range(0,3):
    try:
      num = int(input('Enter a number: '))
      factorial = 1
      if num < 0:
        print('Sorry! Factorials cannot be negative numbers.')
      else:
        for i in range(1, num + 1):
          factorial = factorial*i
        print(num, '!=', factorial)
    except Exception as ex:
        print("Invalid input. Try again")

Answer 2

Wrap your call to int in a try/except block

try:
    foo = int(input())
except Exception:
    print("exception occurred")

this can be made much more advanced with some extra feedback about the error and also arguably better by capturing only the minimum Exception expected

while True:
    _value = input("Enter a number: ")
    try:
        value = int(_value)
    except ValueError:
        print("invalid input!: {}".format(_value)
        continue  # jump to top of loop

Answer 3

The idiomatic way to handle errors in Python is with try: ... except: ... blocks:

for i in range(0,2):
  inp = input('Enter a number: '))
  try:
    num = int(inp)
  except ValueError:
    print('>{}< is not a valid number'.format(num))
    continue
  factorial = 1
  if num < 0:
    print('Sorry! Factorials cannot be negative numbers.')
  else:
    for i in range(1, num + 1):
      factorial = factorial*i
    print(num, '!=', factorial)

Please note that the exception clause should only catch the exception you want to handle. Avoid catch all exception blocks, because they can silently swallow various errors and make some problems harder to diagnose...