Python: check str using regex

Question

I need to write func to check str. If should fit next conditions:

1) str should starts with alphabet - ^[a-zA-Z]

2) str should contains alphabet, numbers, . and - ([\w]+*.-)

3) str should ends with alphabet or number - \w$

4) length of str should be from 10 to 50

def check_login(str):
    flag = False
    if match(r'^[a-zA-Z]([\w]*.-)\w${10, 50}', str):
        flag = True
    return flag

It returns False to all combinations. I think, error in 2 condition. I know, that I can use [a-zA-Z0-9\.-]+, but it does not indicate a mandatory entry.

How can I fix that?

Btw, your function can just be return match(r'^[a-zA-Z]([\w]*.-)\w${10, 50}', str) as that will return the boolean resulting from the match function. No need to define and return flags separately like that. — couragewolf
– couragewolf, Commented Sep 19, 2017 at 15:21
@couragewolf: The regex is wrong. ${10, 50} is a nonsense. — Toto
– Toto, Commented Sep 19, 2017 at 15:22
@Toto yes my bad, I was just making a point on the code, not answering the question — couragewolf
– couragewolf, Commented Sep 19, 2017 at 15:27

Toto · Accepted Answer · 2017-09-19 15:27:38Z

1

Use:

match(r'^[a-zA-Z][\w.-]{8,48}\w$', str)

If you don't want to match _:

match(r'^[a-zA-Z][a-zA-Z0-9.-]{8,48}[a-zA-Z0-9]$', str)

If you want at least one dit, one dash, one letter and one digit:

^[a-zA-Z](?=.*-)(?=.*\.)(?=.*[0-9])[a-zA-Z0-9.-]{8,48}[a-zA-Z0-9]$

Where (?=....) is a lookahead, a zero-length assertion, that makes sure we have its content in the string.

edited Sep 19, 2017 at 15:27

answered Sep 19, 2017 at 15:17

Toto

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3 Comments

RomanPerekhrest Over a year ago

[\w.-] will match ANY of characters, the string should contain ALL of them

Petr Petrov Over a year ago

Can you say, '^[a-zA-Z][\w.-]{8,48}\w$' {8, 48} estimates length part of string before that. But how can I estimate length of str include first and last symbol. I mean if some symbol not important and length of str can starts from 1 symbol?

Toto Over a year ago

@PetrPetrov: [\w.-]{8,48} means from 8 to 48 characters to that, you have to add the first char (a letter) and the last char (aphanum) so the whole length is from 10 to 50 characters. The comments are not the right place to ask new requierements, edit your question or ask a new one because I don't get what you mean in your last sentence especially "some symbol not important"

RomanPerekhrest · Accepted Answer · 2017-09-19 15:42:05Z

1

Straight-forward approach with re.search() function:

import re 

def check_login(s):
    return bool(re.search(r'^[a-zA-Z][a-zA-Z0-9.-]{8,48}[a-zA-Z0-9]$', s)
           and re.search(r'\.[a-zA-Z0-9]*-|-[a-zA-Z0-9]*\.', s[1:-1]))

# test cases
print(check_login('al-De.5af3asd.2'))       # True
print(check_login('3lDe.5af3asd.2'))        # False
print(check_login('al-De.5a'))              # False
print(check_login('xl-De.5a3333333333333')) # True

answered Sep 19, 2017 at 15:42

RomanPerekhrest

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Comments

Ajax1234 · Accepted Answer · 2017-09-19 15:48:19Z

1

You can try this regex:

import re

final_string = [''] if not re.findall("^[a-zA-Z]{1}[a-zA-Z0-9\-\.]{9,49}\d$|\w$", s) else re.findall("^[a-zA-Z]{1}[a-zA-Z0-9\-\.]{9,49}\d$|\w$", s)
if final_string[0] == s:
   #success, a match has been found.
   pass

answered Sep 19, 2017 at 15:48

Ajax1234

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1 Comment

Toto Over a year ago

This doesn't met the 4th requierement "length of str should be from 10 to 50" The first alternative matches 11 to 51 char, the second matches anything that ends with a word character

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