Email Validation code for python not giving expected output

Question

For email validation, i have following conditions: 1. username should be alphanumeric only(a-z,0-9,A-Z) 2. website name should be a-z 3. extension should be a-z

i am writing a python code as :

import re 
def check(email):
    #complete the function
    #the function should return the strings "invalid" or "valid" based on the email ID entered
    if(re.search('^[a-zA-Z0-9]+$@^[a-z]+$.^[a-z]+$',email)):  
        return("valid")  

    else:  
        return("invalid") 


email=input()
print(check(email))

My input: vk@google.com But it returns me "Invalid" It should return as "Valid". What am i doing wrong here?

JvdV · Answer 1 · 2020-03-01T13:52:10.487

4

Your initial pattern will work with:

^[a-zA-Z0-9]+@[a-z]+\.[a-z]+$

Regular expression visualization

Debuggex Demo

You had: ^[a-zA-Z0-9]+$@^[a-z]+~~$.^~~[a-z]+$, where you had:

End string ancor $ midstring *2
Start string ancor ^ midstring *2
Unescaped . which would match any character. Escape with backslash > \.

Regular expression visualization

The above shows why you yield zero matches.

To have control over the amount of alpha characters between @ and the dot you could use:

^[a-zA-Z0-9]+@[a-z]{5,8}\.[a-z]+$

edited Mar 01 '20 at 13:52

answered Mar 01 '20 at 08:53

JvdV

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Thanks JvdV. Couple of doubts...Why are we not using \ for unescaping @ ? Why it it only used for . Because '@' is also being used as a literal character here. And second, what if we want to set a limit to number of characters to be used between @ and . say 5-8 characters only between @ and . – Vandit Mar 01 '20 at 13:39
1

@Vandit. That is because the dot has a special meaning in RegEx and represents and character but newline. The @ has no special meaning. So only characters with special meaning need to be escaped with a backslash to match it literally. And to limit the amount you can say `{5,8}` meaning minimum of 5 and max of 8. I'll update the answer. – JvdV Mar 01 '20 at 13:49
@Vandit. Has this been helpfull and answered your question? If so, consider to click on the checkmark next to the answer to accept the answer and close the question. – JvdV Mar 13 '20 at 09:11

Ahmad · Answer 2 · 2020-03-01T09:23:01.857

2

You can't expect the beginning of the line anywhere in the middle of the line.

                     This is not right
              |         |
'^[a-zA-Z0-9]+$@^[a-z]+$.^[a-z]+$'
                |        |
                       This is the problem

Also, the dot is not escaped, causing the expression to match any character. If you want it to match a literal dot, then you have to proceed it with a slash. Change that to

'^[a-zA-Z0-9]+@[a-z]+\.[a-z]+$'

edited Mar 01 '20 at 09:23

answered Mar 01 '20 at 09:21

Ahmad

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There are more problematic ancors + an unescaped dot. =). Basically what I wrote down in my answer. – JvdV Mar 01 '20 at 09:22

Email Validation code for python not giving expected output

2 Answers2