[Python] Regex matching with negative look-behind assertion

I am parsing C source files. I want to match all the variables (in snake-case format) that end in _VALUE and don't begin with CANA_, CANB_... ,CANF_. I need to match the whole variable name for later substitution.

This is my current setup with python

import re

def signal_ending_VALUE_updater(match: re.Match) -> str:
groups = match.groupdict()
return some_operation_on(group["SIGNAL_NAME"])

REGEX=r"(?<!CAN[A-F]_)\b(?P<SIGNAL_NAME>\w+_VALUE)\b"

with open(file_path,'r') as f:
content = f.read()
content_new = re.sub(REGEX,signal_ending_VALUE_updater,content)


Unfortunately this regex doesn't work all the times, for example if we try this testacase

test=" shared->option.mem = ((canAGetScuHmiVehReqLiftModBtnSt() == CANA_SCU_HMI_VEH_REQ_LIFT_MOD_BTN_ST_PRESSED_VALUE) ||"
re.find(REGEX,test)


Will return the variable (CANA_SCU_HMI...) that I don't want to match. What am I not considering in the regex?

The idea behind the regex is:

• (?<!CAN[A-F]_): with a negative-lookbehind ensure the match does not start with CAN followed by one of the letters A, B, C, D, E, or F, and an underscore (_).
• \b: word boundary, ensuring that we are matching whole words and not one part of a word
• (?P<SIGNAL_NAME>\w+_VALUE):
  • (?P<SIGNAL_NAME>...): group match with the name SIGNAL_NAME
  • \w same as [a-zA-Z0-9_] will match snakecase variable names
  • + ensures one or more of before
  • _VALUE matches the literal string _VALUE at the end of the variable name.
• \b This again is a word boundary that ensures the match ends right after the variable name.

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