使用正则表达式验证用户输入是一个整数

Question

I am trying to validate a user's input. I only want the user to be able to enter a positive or negative integer. All other inputs (ie anything with letters) should be rejected

I have the code below at the minute, however I am getting an error. I'm assuming it has to do with the data types but am unsure how to fix this.

import re

number =input("Please enter a number: ")
number=int(number)
while not re.match("^[0-9 \-]+$", number):
    print ("Error! Make sure you only use numbers")
    number = input("Please enter a number: ")
print("You picked number "+ number)

Answer 1

If all you care about is that the input was a valid numeric literal, don't even bother with the regexp. int will correctly parse the string or raise an exception.

while True:
    s = input("Please enter a number: ")
    try:
        n = int(s)
        break
    except ValueError:
        print("Error! Make sure you only use numbers")
print("You picked number " + n)

Answer 2

Regular expressions need strings as input, not numbers. Thus, you do not have to cast the string to number, and you can omit number=int(number) .

Here is a working demo :

number = "2"
if not re.match("^[0-9 -]+$", number):
    print ("Error! Make sure you only use numbers")
print("You picked number "+ number)

Answer 3

import re

while  True:
    number =input("Please enter a number: ")
       # number=int(number) -- This raise an error, for regexp you need use "str"

    #while not re.match("^[0-9 \-]+$", number):
    # in [0-9 \-]  after 9 you use whitespace
    # Also in [0-9 \-]  if minus at the and, not need use backslash

if  re.match("-?\d+$", number) : # minus may be only in first position
    break

print ("Error! Make sure you only use numbers")
    # deleted     number = input("Please enter a number: ")

print("You picked number "+ number)

Answer 4

answer = input(" ")#asks the user for an answer
ansnum = re.match("[0-9 \-]",answer)#checks to see if answer only contains numbers
while not ansnum: #whilst the answer does not contain numbers do....
   answer = input("Enter numbers as your answer: ")#asks the user for a valid answer
   ansnum = re.match("[0-9 \-]",answer)#checks to see if the answer contains numbers