你可以完全去掉正则表达式，字符串对象的计数方法就足够了，其他很多代码也可以简化.

You can get rid of the regex entirely, the count-method of string objects is enough, much of the other code can be simplified as well.

您也没有将数据更改为小写，只是将字符串打印为小写，请注意我如何使用 data = data.lower() 实际更改变量.

You're also not changing data to lower case, just printing the string as lower case, note how I use data = data.lower() to actually change the variable.

试试这个代码:

import glob
import os

path = 'c:\script\lab\Tests'

k = 0

substring = ' at least '
for filename in glob.glob(os.path.join(path, '*.txt')):
    if filename.endswith('.txt'):
        f = open(filename)
        data = f.read()
        data = data.lower()
        S= data.count(substring)
        if S:
            k= k + 1
            print("'{}' match".format(filename), S)
        else:
            print("'{}' no match".format(filename))
print("Total number of matches", k)

如有任何不清楚的地方，请随时提问！

If anything is unclear feel free to ask!