Try this, based on How do I list all files of a directory?
import os, time
def last_mod_today(path):
    '''
    return True if getmtime and time have year, mon, day coincinding in their localtime struct, False else
    '''
    t_s = time.localtime(os.path.getmtime(path))
    today = time.localtime(time.time())
    return t_s.tm_mday==today.tm_mday and t_s.tm_year == today.tm_year and t_s.tm_mon == today.tm_mon
name_to_path = lambda d,x:os.path.normpath(os.path.join(os.path.join(os.getcwd(), d),x))
def log_files(d):
    '''
    walking through the files in d
    log the content of f when last modif time for f is today
    WARNING : what happens when the file is a JPEG ?
    '''
    scand_dir = os.path.join(os.getcwd(), d)
    print(f"scanning {scand_dir}...")
    (_, _, filenames) = next(os.walk(scand_dir))
    log = open("log.txt", 'a')
    for f in filenames:
        if last_mod_today(name_to_path(d,f)):
            with open(name_to_path(d,f), 'r') as todays_file:
                log.write('##############################\n')
                log.write(f"file : {name_to_path(d,f)}\n")
                log.write(todays_file.read()) 
                log.write('\n')
                log.write('##############################\n')
    log.close()
#first scanning files in the current directory
(_, dirnames, _) = next(os.walk('./'))
log_files('./')
#then crawling through the subdirs (one level)
for d in dirnames:
    log_files(d)