CODEWITHSUNDEEP
pythonlistindexingweb.pyerror-list
Antonio E.
Antonio E.

Reputation: 359

list Index error

I have this method in a class which takes a value from a database call, (the table in the database has a key: catId and another field)

def getCat(self):
        ''' devuelve el numero de la categoria
        '''
        a = self.datab.select('categorias',where='catName = $nombre', vars=dict(nombre=self.nombre))
        a= a.list()
        return a[0].catId

    context: i use this to make some categorization in my web content, so i want to return the value wich will join to the content table in the database.

So if i give to it a self.nombre wich is a string stored in a database row i'll ever take one element from the database.

The python interpreter gives me this error:

  File "C:\xampp\htdocs\webpy\functions.py", line 26, in getCat
    return a[0].catId
IndexError: list index out of range

127.0.0.1:51463 - - [05/Apr/2013 13:29:22] "HTTP/1.1 GET /c/\css\style.css" - 500 Internal Server Error

but the web gives out the information correctly, I have no problem with the web output but i wish to know why is this error in the indexing a[0]

I made the a.list() in order to simplify some uses of the itterbetter

complete error mesage in the idle interpreter:

0.0 (1): SELECT catName FROM categorias ORDER BY catId ASC 
127.0.0.1:51900 - - [05/Apr/2013 16:46:31] "HTTP/1.1 GET /c/" - 200 OK
0.0 (1): SELECT * FROM categorias WHERE catName = '\\css\\style.css'
Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\web\application.py", line 236, in process
    return self.handle()
  File "C:\Python27\lib\site-packages\web\application.py", line 227, in handle
    return self._delegate(fn, self.fvars, args)
  File "C:\Python27\lib\site-packages\web\application.py", line 409, in _delegate
    return handle_class(cls)
  File "C:\Python27\lib\site-packages\web\application.py", line 384, in handle_class
    return tocall(*args)
  File "C:\xampp\htdocs\webpy\code.py", line 32, in GET
    seleccion = functions.categoria(db,cat)
  File "C:\xampp\htdocs\webpy\functions.py", line 16, in __init__
    self.n = self.getCat() #calculo del numero de la categoria PROBLEMAS
  File "C:\xampp\htdocs\webpy\functions.py", line 26, in getCat
    return a[0].catId
IndexError: list index out of range

Upvotes: 0

Views: 360

Answers (2)

vivek
vivek

Reputation: 2867

You need to do proper error handling, you can either do:

try:
    a[0].catId
except IndexError as ie:
    # Do some stuff here
except:
    # either re-raise the exception or pass it silently

Or you can do:

return a and a[0].catId or [] # This will check for empty list

It depends on your implementation choice.

Upvotes: 3

mgilson
mgilson

Reputation: 309891

That's the exact error message you would get if you tried to get an item from an empty list:

>>> [][0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range

So it appears that a.list() is returning an empty list.

Upvotes: 1

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