scoping problem with list comprehension // learning Python

[Adrian Dragulescu]

I just started to learn python (first posting to the list).

I have a list of dates as strings  that I want to convert to a 
list of datetime objects.  Here is my debugging session from inside a 
method.

(Pdb) formatIndex
'%Y-%m-%d'
(Pdb) [datetime.strptime(i, formatIndex) for i in self.index[0:3]]
*** NameError: global name 'formatIndex' is not defined
(Pdb) [datetime.strptime(i, '%Y-%m-%d') for i in self.index[0:3]]
[datetime.datetime(2007, 1, 3, 0, 0), datetime.datetime(2007, 1, 4, 0, 0), 
datetime.datetime(2007, 1, 5, 0, 0)]
(Pdb)

How come I get an error that formatIndex is not defined? I just show that 
it has value '%Y-%m-%d', in the same method scope.  Not sure why it says 
"global name", as I am in a method.

If I run it as a stand-alone, it works:
   index = ['2007-01-01', '2007-01-02', '2007-01-03']
   formatIndex = '%Y-%m-%d'
   print([datetime.strptime(i, formatIndex) for i in index])

Any suggestions much appreciated.  I'm sure it's something trivial.  I'm 
using Python30.

Adrian