title: Regex in Python to match all the files in a folder
body: <p>I'm very bad at regex. 
  I'm trying to locate files in a folder based on the file names. Most of the filenames are in the format <code>GSE1234_series_matrix.txt</code>, hence I've been using <code>os.path.join("files", GSE_num + "_series_matrix.txt")</code>. However, a few files have names like <code>GSE1234-GPL22_series_matrix.txt</code>. I'm not sure how to address all the files starting with a GSE number and ending with _series_matrix.txt together, possibly in one statement. I'd really appreciate any help. </p>
  
  <p>EDIT - I have these series matrix text files in a folder, for which I mention the path using path join. I also input a text file, which has all the GSE numbers. This way it runs the script only for selected GSE numbers. So not everything that's in the folder is in GSE num list AND the list just has GSE numbers and not GPL. For instance the file GSE1234-GPL22_series_matrix.txt would be GSE1234 in the list.</p>