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How to create regex to match a string that contains only hexadecimal numbers and arrows?

December 14, 2022

I am using a string that uses the following characters:

0-9    
a-f    
A-F    
Greater Than, Hyphen

The mixture of the greater than and hyphen must be:

->
-->

Here is the regex that I have so far:

[0-9a-fA-F\-\>]+

I saw on multiple websites that to have an exclusion(g-zG-Z, other special characters) you would use ^ but I tried to do the following and it did not work:

[^g-zG-Z][0-9a-fA-F\-\>]+
^g-zG-Z[0-9a-fA-F\-\>]+
[0-9a-fA-F\-\>]^g-zG-Z+
[0-9a-fA-F\-\>]+^g-zG-Z
[0-9a-fA-F\-\>]+[^g-zG-Z]

Just to be extra clear since this is a larger question I want my regex to contain:

a-z
A-Z
0-9
Hyphen and Greater than in the order of "->" or "-->"

I test all of the regex using:

import re as regex
regex.match(regex.compile("REGEX"),"String")

Here are some samples:

"0912adbd->12d1829-->218990d"
"ab2c8d-->82a921->193acd7"

>Solution :

Firstly, you don’t need to escape - and >

Here’s the regex that worked for me:
^([0-9a-fA-F]*(->)*(-->)*)*$

Here’s an alternative regex:
^([0-9a-fA-F]*(-+>)*)*$

What does the regex do?

^ matches the beginning of the string and $ matches the ending.
* matches 0 or more instances of the preceding token
Created a big () capturing group to match any token.
[0-9a-fA-F] matches any character that is in the range.
(->) and (-->) match only those given instances.

Putting it into a code:

import re
regex = "^([0-9a-fA-F]*(\-\>)*(\-\-\>)*)*$"
re.match(re.compile(regex),"0912adbd->12d1829-->218990d")
re.match(re.compile(regex),"ab2c8d-->82a921->193acd7")
re.match(re.compile(regex),"this-failed->so-->bad")

You can also convert it into a boolean:

print(bool(re.match(re.compile(regex),"0912adbd->12d1829-->218990d")))
print(bool(re.match(re.compile(regex),"ab2c8d-->82a921->193acd7")))
print(bool(re.match(re.compile(regex),"this-failed->so-->bad")))

Output: