python语句整理
pass语句，可在代码块中使用它来让Python什么都不要做。
pass语句还充当了占位符，它提醒你在程序的某个地方什么都没有做，并且以后也许要在这
里做些什么。
def count_words(filename):
try:
with open(file_name) as file_object:
contents = file_object.read()
except FileNotFoundError:
pass
else:
file_words = contents.split()
file_words_nums = len(file_words)
print("The file "+file_name+" has about "+str(file_words_nums)+" words.")
file_names = [‘guest_book.txt‘,‘book.txt‘,‘guest.txt‘]
for file_name in file_names:
count_words(file_name)