使用Boto上传目录时设置Content-Type键

I am using os.walk to get a directory of files and then using the boto suggested way of uploading large files. From what I have read, I need to set the content-type key at upload time, but the directory has multiple file types that need different content-type keys. Any suggestions on how to get the proper content-type for each file so it can be set in the key? Mime types library? Something else?I am using os.walk to get a directory of files