title: Python + regex: How to extract values between two underscores in Python?
body: <p>I am trying to extract values between two underscores. For that I have written this code:</p>
  
  <pre><code>patient_ids = []
  for file in files:
      print(file)
      patient_id = re.findall("_(.*?)_", file)
      patient_ids.append(patient_id)
  
  print(patient_ids) 
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>PT_112_NIM 26-04-2017_merged.csv
  PT_114_NIM_merged.csv
  PT_115_NIM_merged.csv
  PT_116_NIM_merged.csv
  PT_117_NIM_merged.csv
  PT_118_NIM_merged.csv
  PT_119_NIM_merged.csv
  [['112'], ['114'], ['115'], ['116'], ['117'], ['118'], ['119'], ['120'], ['121'], ['122'], ['123'], ['124'], ['125'], ['126'], ['127'], ['128'], ['129'], ['130'], ['131'], ['132'], ['133'], ['134'], ['135'], ['136'], ['137'], ['138'], ['139'], ['140'], ['141'], ['142'], ['143'], ['144'], ['145'], ['146'], ['147'], ['150'], ['151'], ['152'], ['153'], ['154'], ['155'], ['156'], ['157'], ['158'], ['159'], ['160'], ['161'], ['162'], ['163'], ['165']]
  </code></pre>
  
  <p>So extracted values are in this form: ['121']. I want them in this form: 121 , i.e., just the number inside two underscores. </p>
  
  <p>What change should I make to my code?</p>