old_contents: #!/usr/bin/python3
  ################################################################################
  # otp.py - Google OTP generator with secret stored on Yubikey
  #
  # author: mutantmonkey <mutantmonkey@mutantmonkey.in>
  ################################################################################
  
  import binascii
  import hashlib
  import hmac
  import struct
  import subprocess
  import time
  
  PASS_CODE_LENGTH = 6
  INTERVAL = 30
  ADJACENT_INTERVALS = 1
  PIN_MODULO = 10**PASS_CODE_LENGTH
  
  def get_timestamp():
      return int(time.time() / INTERVAL)
  
  def make_pin(resp):
      offset = resp[-1] & 0x0F
      resp = resp[offset:offset + 4]
      pin = struct.unpack('>L', resp)[0]
      pin &= 0x7FFFFFFF
      pin %= PIN_MODULO
      return '{0:06d}'.format(pin)
  
  def challenge_yubikey():
      tm = get_timestamp()
      tm = struct.pack('>q', tm)
  
      chal = binascii.hexlify(tm)
      resp = subprocess.check_output(['ykchalresp', '-2x', chal])
      resp = resp.strip()
      resp = binascii.unhexlify(resp)
  
      print(make_pin(resp))
  
  if __name__ == "__main__":
      challenge_yubikey()
  
new_contents: #!/usr/bin/python3
  ################################################################################
  # otp.py - Google OTP generator with secret stored on Yubikey
  #
  # author: mutantmonkey <mutantmonkey@mutantmonkey.in>
  ################################################################################
  
  import binascii
  import hashlib
  import hmac
  import struct
  import subprocess
  import time
  
  PASS_CODE_LENGTH = 6
  INTERVAL = 30
  PIN_MODULO = 10**PASS_CODE_LENGTH
  
  def get_timestamp():
      return int(time.time() / INTERVAL)
  
  def make_pin(resp):
      offset = resp[-1] & 0x0F
      resp = resp[offset:offset + 4]
      pin = struct.unpack('>L', resp)[0]
      pin &= 0x7FFFFFFF
      pin %= PIN_MODULO
      return '{0:06d}'.format(pin)
  
  def challenge_yubikey():
      tm = get_timestamp()
      tm = struct.pack('>q', tm)
  
      chal = binascii.hexlify(tm)
      resp = subprocess.check_output(['ykchalresp', '-2x', chal])
      resp = resp.strip()
      resp = binascii.unhexlify(resp)
      print(make_pin(resp))
  
  if __name__ == "__main__":
      challenge_yubikey()
  
subject: remove unused variable