eem_regex.py

import  re

SRC = 'no event manager applet test\nevent manager applet test\n event none\n action 1010 if 1 eq 1\n action 1020  set i 1\n action 1030 end\n! end_applet\n'

NO_APPLET = ''
LABEL = '^ action \d{4}'
LABEL_START = 10
LABEL_STEP = 10

print(SRC)

dst = ''
label = LABEL_START
repl = ' action ' + '{:04d}'.format(label)
# repl = 'action ' + str(label)

# prog = re.compile(LABEL)
# result = prog.match(string)

for line in SRC.splitlines():
    newline, i = re.subn(LABEL, repl, line)
    # re.subn(pattern, repl, string, count=0, flags=0)
    if i > 0:
        label = label + LABEL_STEP
        # repl = ' action ' + format('{%4d}', label)
        repl = ' action ' + '{:04d}'.format(label)
        # repl = 'action ' + str(label)

    dst = dst + newline + '\n'

print(dst)