过滤掉较大字符串中的特定字符串？

I'm new to Python and after this one script I probably won't work with Python at all. I'm extracting some data using Scrapy and have to filter out some string (I've already done this with digits using isdigit()). Googling gives me pages about filtering out special strings, but what I want is really just a small part of a larger string.I'm new to Python and after this one script I p