[BEGIN_PATTERN]
    line1=abd;
    line2=ZXY;
    ...
    line43=454;
    ...
    ...
[END_PATTERN]
[BEGIN_PATTERN]
    line1=abc;
    line2=ZXC;
    ...
    line72=847;
    ...
[END_PATTERN]
[BEGIN_PATTERN]
    line1=abe;
    line2=ZXV;
    ...
    line33=135;
    ...
[END_PATTERN]
[BEGIN_PATTERN]
    line1=abt;
    line2=ZXF;
    ...
    line54=734;
    ...
[END_PATTERN]

abd,ZXY,aaa,454,ggg,ggs
abc,ZXC,mgf,847,jde,g3e
abe,ZXV,ytd,135,dfs,jhf
abt,ZXF,ytf,734,ytd,hge

import re

START_PATTERN = '<BEGIN'
END_PATTERN = '<BEND'

with open('DB_example.txt') as file:
    match = False
    newfile = None

    for line in file:
        if re.match(START_PATTERN, line):
            match = True
            newfile = open('my_new_file.txt', 'w')
            continue
        elif re.match(END_PATTERN, line):
            match = False
            newfile.close()
            continue
        elif match:
            #remove TAB and BreakLine
            valor=line.rstrip().replace('t','')
            #split Key and value
            (key, val) = valor.split('=')
            if re.match('line1',key):
                match = True
                #before write into file remove ";"
                newfile.write(val.replace(';',''))
                continue
            elif re.match('line2',key):
                match:False
                newfile.write(','+val.replace(';', ''))
                continue
            elif re.match('lineXX',key):
                match:False
                newfile.write(','+val.replace(';', ''))
                continue
            elif re.match('lineYY',key):
                match:False
                newfile.write(','+val.replace(';', ''))
                continue