如果拆分列表中的值为空，则返回False

Question

I'm working on a script that allows users to input an email. If the email has a 'username' and 'domain' such as username@domain.com, then the program should output that the email is an email. If the user enters something such as username@, then the program should output that the input is not a valid email address.

The function should return True when the text is an email, otherwise it should return False.

I'm having a problem getting the program to return False when entering an address like 'username@' or '@gmail.com'.

I currently have the following code:

text = ''
tokens = 0
split_counter = 0

def isEmail(text):
    tokens = text.split('@')
    split_counter = len(tokens)
    if split_counter == 2:
        print(text, '==> EMAIL')
    else:
        print(text, '==> NOT EMAIL')
    return

while True:
    text = input("Email: ")    
    if text == 'quit':
        print('Later!')
        break
    else:
        isEmail(text)

Thank you.

Answer 1

I would recommend using regex and looking at the other answers on StackOverflow for checking for a valid email. But in response to your question, from what you commented above, it is not returning false when you try "@gmail.com". This is because when you split a string by "@", it returns

string = "@gmail.com"
string.split("@")
>>> ['', 'gmail.com']

Therefore, the length of that returned list will be 2. You could make another check inside the split_counter list:

if split_counter == 2 and tokens[0] != '':
    print(text, '==> EMAIL')

I would recommend printing whatever you have along the way as a way of debugging your code. It'll help you avoid errors like this in the future. You knew that the condition had to be wrong, and the condition is only dependent on split_counter, so you could have printed split_counter to see what went wrong.

Answer 2

The split method always return two strings if there is only one @ . For example:

>>> text="foo@"
>>> text.split('@')
['foo', '']

So you should check that the two returned strings have a length greater than zero.

Answer 3

You can see the problem is split() function:

>>> text = "@gmail.com"
>>> tokens = text.split("@")
>>> tokens
['', 'gmail.com']

Best practice is to use regex to check valid emails instead of writing hard code:

def isEmail(text):
    if len(text) > 6:
        if re.match(r'\b[\w.-]+@[\w.-]+.\w{2,4}\b', text) != None:
            # do something
    else:
        # do something

If you don't know what is regex , then this is probably the right time to learn it.

Answer 4

A simple solution could be to leverage all() and the fact, that bool("") is False for that:

>>> email = "@gmail.com"
>>> s = email.split("@")
>>> all(s)
>>> False

>>> email = "a@"
>>> s = email.split("@")
>>> all(s)
>>> False

>>> email = "a@gmail.com"
>>> s = email.split("@")
>>> all(s)
>>> True

But beware, that this code doesn't say anything about the "correctness" of an email adress. It only says something about whether a string could be split by @ and none of the parts is empty.

For that purpose I would rely on validators provided by frameworks like Django or something like WTForms .

Answer 5

All you're missing is another check on line 11:

if split_counter == 2 and len(tokens[0]) > 0 and len(tokens[1]) > 0:
    print(text, '==> EMAIL')