Regex expression to check if string obeys certain conditions

Question

I need to write a python function that takes a string, and uses REGEX to check if the string contains:

At least 1 uppercase letter;
At least 2 numerical digits;
Exactly 2 special characters, !@#$&*-_.
A length of 6-8 characters;

Returns true if these exist and false otherwise. I'm good with the function, however, I'm having trouble with the regular expression.

What I have so far is: [A-Z]+\d{2,}[!@#\$&\*-_\.]{2}

I know this doesn't work, I'm really confused since I'm new to regex.

Thanks for your help!

Do you have to put all those conditions into a single regex? Or can you break it into one regex for each condition? — John Gordon
– John Gordon, Commented Nov 28, 2020 at 6:36
@John Gordon Nope they don't all have to be in a single regex :) — Segmentation Fault
– Segmentation Fault, Commented Nov 28, 2020 at 6:41

The fourth bird · Accepted Answer · 2020-11-28 13:43:07Z

3

You can use

^(?=[^A-Z\r\n]*[A-Z])(?=[^\d\r\n]*\d[^\d\r\n]*\d)(?=.{6,8}$)[A-Z\d]*[!@#$&*_.-][A-Z\d]*[!@#$&*_.-][A-Z\d]*$

Note to escape the \- in the character class or place it at the start or end. Else it would denote a range.

Explanation

^ Start of string
(?=[^A-Z\r\n]*[A-Z]) Positive lookahead, assert a char A-Z
(?=[^\d\r\n]*\d[^\d\r\n]*\d) Positive lookahead, assert 2 digits
(?=.{6,8}$) Positive lookahead, assert 6 - 8 characters in total
[A-Z\d]*[!@#$&*_.-][A-Z\d]*[!@#$&*_.-][A-Z\d]* Match 2 "special" characters
$ End of string (Or use \Z if there can no newline following)

Regex demo

answered Nov 28, 2020 at 13:43

The fourth bird

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2 Comments

Segmentation Fault Over a year ago

This is perfect! Only problem is it doesn't match if I have any lowercase characters in the string. Like for example the string "A00!$a" is supposed to match. Do you know what I can do to fix this?

The fourth bird Over a year ago

@SegmentationFault You can add a-z to the matching character class, see regex101.com/r/5zbejo/1

PaxPrz · Accepted Answer · 2020-11-28 07:11:20Z

2

This regex should work for you in python

^(?=.*[A-Z])(?=.*[0-9].*[0-9])(?=.*[!@#$%^&*()_+,.\\\/;':\"-].*[!@#$%^&*()_+,.\\\/;':\"-]).{6,8}$

Here is the test run in regex101

edited Nov 28, 2020 at 7:11

answered Nov 28, 2020 at 7:01

PaxPrz

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3 Comments

Segmentation Fault Over a year ago

Thanks a lot, this works! except for a few things: 1. I just changed the end to .{6,8} (to allow lenghts between 6 and 8). 2. This expression requires that I have atleast one small character, which isnt part of the requirements. But this a great start I can probably figure it out! thanks!

Segmentation Fault Over a year ago

Also I just noticed one more thing, it lets me put in as many special chars as I want whereas its only asking for exactly 2

Toto Over a year ago

@Segmentation Fault: Be aware that matches A12!!*$@, more than 2 special characters.

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