import os
 statinfo = os.stat('1.txt')
 statinfo
os.stat_result(st_mode=33206, st_ino=177892185281212675, st_dev=3126555808, st_nlink=1, st_uid=0, st_gid=0, st_size=9, st_atime=1518466873, st_mtime=1518467077, st_ctime=1518466873)
>>> statinfo.st_size
9

 #
import os
txt_file_list = [file_name for file_name in os.listdir() if ".txt" in file_name]
txt_file_size_list = map(os.path.getsize, txt_file_list)
print(sum(txt_file_size_list))