(Python) Shelve + try: how to search for a key and set it if it doesn't exists without repeating code?

Question

To store the user work folders permanently, I'm using shelve. And to know if the user has the folders configured I'm using a similar code 3 times:

pastaUsuario = os.getenv('HOMEDRIVE') + os.getenv('HOMEPATH')
pastaPrincipal = pastaUsuario + '\\rev'
pastaConfig = pastaPrincipal + '\\config'

config = shelve.open(pastaConfig + '\\config.db')
try:
  pastaIsometricosSpooler = config['pastaIsometricosSpooler']
except Exception:
  config['pastaIsometricoSpooler'] = raw_input('Digite o caminho da pasta de extração do       Spooler: ')
  pastaIsometricosSpooler = config['pastaIsometricosSpooler']
finally:
  config.close()

config = shelve.open(pastaConfig + '\\config.db')  
try:
  ultimoIso = config['ultimoIso']
except Exception:
  config['ultimoIso'] = raw_input('Digite o tag do isométrico a ser revisado: ')
  ultimoIso = config['ultimoIso']
 finally:
  config.close()

config = shelve.open(pastaConfig + '\\config.db')
try:
  ultimaRev = config['ultimaRev']
except Exception:
  config['ultimaRev'] = raw_input('Digite a nova revisão: ')
  ultimaRev = config['ultimaRev']
finally:
  config.close()

How to avoid repeating the almost identical code? I tried to use the "for" statement with a list:

config = shelve.open(pastaConfig + '\\config.db')
for x in ['pastaIsometricosSpooler', 'ultimoIso', 'ultimaRev']:
  try:
    x = config[x]
  except Exception:
    config[x] = raw_input()
    x = config[x]
  finally:
    config.close()

But the variable set doesn't work because of quotes (eg.: 'ultimaRev' = config['ultimaRev'])

Sorry for my bad english!

Answer 1

This is probably best done by using a function rather than trying to make the same code work in a loop. Adapting what you have:

def getconfig( x, prompt ):   
  try:
    theconf= config[x]
  except Exception:
    config[x] = raw_input( prompt )
    theconf= config[x]
  return theconf

Then you can use it three times:

config = shelve.open(pastaConfig + '\\config.db')
ultimaRev = getconfig( 'ultimaRev', 'Digite a nova revisão: ')
ultimoIso = getconfig( 'ultimoIso', 'Digite o tag do' )
pastaIsometricosSpooler = getconfig('pastaIsometricosSpooler', 'Digite o caminho da' )
config.close()