Converting a list of string to list of integer

Try something like this:

>> a = ['1', '2', '']
>>> def toint(s, default=0):
...     try:
...         return int(s)
...     except ValueError:
...         return default
...
>>> [toint(x) for x in a]
[1, 2, 0]
>>>

This has the added benefit of conforming to Python's Duck Typing idiom and giving you the flexibility to change the default if processing your data results in a ValueError exception. e.g:

>>> [toint(x, None) for x in a]
[1, 2, None]

You could just write a function that makes use of int and then have a fallback condition on failures that does what you want for a input string, then call that function in the list comprehension statement.

example:

def converter(ele):
    # result = your integer conversion logic
    return result

a = [converter(ele) for ele in elements]

Use a dict to handle your unusual values

a = [int({'NAN': '-1', '': 0}.get(i, i)) for i in a] 

Modifying your list comprehension a little as:

a = [int(ele) if ele else 0 for ele in a]

gives what you want. This will work if the non number is a '' not if it is a NAN. If 'NAN' is part of the list, this will do it:

a = [int(ele) if ele != 'NAN' else 0 for ele in a]

>>> a = ['1', '2', '', 'NAN']

>>> listofInt =  map(lambda s: int(s) if s not in 'NAN' else  -1 if s == 'NAN' else 0, a)

>>> print listofInt

>>> [1, 2, 0, -1]

You could write a lambda function even as a anonymous function.

>>> a = ['1', '2', 'NAN', '']
>>> 
>>> def to_int(value):
...     try:
...         return int(value)
...     except ValueError:
...         if value == 'NAN':
...             return -1
...         return 0
... 
>>> [to_int(x) for x in a]
[1, 2, -1, 0]
>>> 

def convert(myList):
    newList = [0]*len(myList)
    for i in range(len(myList)):
        try:
            newList[i] = int(myList[i])
        except:
            newList[i] = -1
    return newList

obviously this try/except just puts -1 for anything that can't be converted to an integer

easily converted to a more specific if myList[i]=='NAN': newList[i]=-1