Substitution with regular expression returns hidden character SOH

[bajacri]

Hello community, hope everyone is having a good time.

I'm doing a pretty easy script, look for a certain format of values in a file then repeat them three times in an output file.

Example:
Find -> 0.875*V
Substituted -> =0.875*V<TAB>=0.875*V<TAB>=0.875*V<TAB>

This regular expression already has worked us in Perl but I have not been able to figure out why it fails in Python.

From the results I can see the group is captured correctly but it is substituted with SOH character(Start Of Header) instead of captured value.

Our work environment:
- Windows 10 Pro
- Python 3.8

import re
from pathlib import Path

FILEHANDLER_R = open( "input.txt", "r" )
FILEHANDLER_W = open( "output.txt", "w" )

for line in FILEHANDLER_R:
	line = re.sub( "\t(\d*\.*\d*\**V*)", "\t=\1\t=\1\t=\1", line )
	print( line )
	FILEHANDLER_W.write( line )
	

FILEHANDLER_R.close()
FILEHANDLER_W.close()

Input file is:

vdd_0p9_hsio_ebipll 0.875*V 0.875*V 0.920*V 1.1*V 1.1*V 0.830*V 0.830*V 0.830*V 0.875*V

Output file results:

Output:
vdd_0p9_hsio_ebipll	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=
	=

Any ideas you can share with us is greatly appreciated.

Thanks for the time reading this post.

[snippsat]

>>> s = '\t=\1'
>>> s
'\t=\x01'
>>> print(s)
	=

>>> 
>>> # Fix
>>> s = r'\t=\1'
>>> s
'\\t=\\1'
>>> print(s)
\t=\1

Always use raw string r with regex because of escape characters.

>>> import re
>>> 
>>> data = 'vdd_0p9_hsio_ebipll	0.875*V	0.875*V	0.920*V	1.1*V	1.1*V	0.830*V	0.830*V	0.830*V	0.875*V'
>>> line = re.sub(r"\t(\d*\.*\d*\**V*)", r"\t=\1\t=\1\t=\1", data)
>>> print(line)

Output:
vdd_0p9_hsio_ebipll	=0.875*V	=0.875*V	=0.875*V	=0.875*V	=0.875*V	=0.875*V	=0.920*V	=0.920*V	=0.920*V	=1.1*V	=1.1*V	=1.1*V	=1.1*V	=1.1*V	=1.1*V	=0.830*V	=0.830*V	=0.830*V	=0.830*V	=0.830*V	=0.830*V	=0.830*V	=0.830*V	=0.830*V	=0.875*V	=0.875*V	=0.875*V

[bajacri]

Hi snippsat.

Thank you for your answer, straight to the point.

I definitely need to read about these raw strings.