Email 使用 re.search 进行验证 Python

Question

Need help making email verifications with the variable 'pattern' and making it so that it loops if it doesn't contain whatever is within the pattern. Required to use re.search. I tried a couple of things for the last hour and this is where I'm kind of lost.

import re
pattern = '[a-zA-Z0-9]' + '[a-zA-Z0-9]'+'@[a-zA-Z]'+'(.com/.edu/.net)'
user_input = input('Enter Your Email:')
while user_input is not pattern:
    if (re.search(pattern,user_input)):
        print(re.seach(pattern,user_input))
        print('Valid Email:'+ user_input)
    else:
        print(re.search(pattern,user_input))
        print('Invalid Email:'+ user_input)
        user_input = input('Enter Your Email:')```

Answer 1

The code is great, but the pattern lacks a bit of functionality. In fact for e-mail addresses, it misses the dash - and the underscore _ . Luckily, you can just say to match \w . It is the same as if you would have specified [a-zA-Z0-9_] . (it still misses the dash though, so your approach is good but too short.) Anyway, there are a few further things that an address should meet.

1. it must start with a alphabetic character
2. While theoretically, the address could be composed of a single character at the start and only to after the @ sign, and be almost infinitely long, it is highly unlikely

I suggest the pattern '[a-zA-Z]+[a-zA-Z0-9_\-]{0,42}@[a-zA-Z]{2,42}\.((com)|(edu)|.net))\b?'

Limiting the number of characters with '{m,n}' lets you ensure that you won't have an overflow error when storing the address. Well and addresses shorter than 'a@bc.st' simply don't exist as at least two characters are required.

Lastly, the or-operator applies only to the immediate adjoin characters, so you need to group the mail extensions: ((com)|(edu)|.net))

import re
pattern = '[a-zA-Z]+[a-zA-Z0-9_\-]{0,42}@[a-zA-Z]{2,42}\.((com)|(edu)|(net))\b?'
while True:
  user_input = input('Enter Your Email:')
  if re.match(pattern, user_input):
      print(re.search(pattern,user_input))
      print('Valid Email:'+ user_input)
      break
  else:
      print(re.match(pattern,user_input))
      print('Invalid Email:'+ user_input)

I think, it is better if you use re.match() as it matches the string right from the start. Usually one doesn't like if you end up with 1abc@def.comm to be a valid address (because re.search() would find the valid string abc@def.com . With the same argumentation, you should add a \b to the end of the pattern

Answer 2

I made a slight modification to your pattern and to your code.

import re
pattern = '[a-zA-Z0-9]+@[a-zA-Z]+(\.com|\.edu|\.net)'
while True:
  user_input = input('Enter Your Email:')
  if (re.search(pattern,user_input)):
      print(re.search(pattern,user_input))
      print('Valid Email:'+ user_input)
      break
  else:
      print(re.search(pattern,user_input))
      print('Invalid Email:'+ user_input)
     

Here's an example run:

Enter Your Email:fred
None
Invalid Email:fred
Enter Your Email:mark@so.com
<re.Match object; span=(0, 11), match='mark@so.com'>
Valid Email:mark@so.com