mosscliffe schreef:

The first argument to map is a function, which is called with the items
of the argument sequences. If the first argument is None, a default
function is used which returns a tuple of the items. In the case that
two input sequences are provided:

map(None, lista, listb)

is equivalent to:

def maketuple(a, b):
     return a, b
map(maketuple, lista, listb)

So what you want to do can be done with map like this:

def make_fill_missing(fillchars):
     def fill_missing(a, b):
         if a is None:
             a = fillchars
         if b is None:
             b = fillchars
         return a, b
     return fill_missing

map(make_fill_missing("N/A"), lista, listb))

--
If I have been able to see further, it was only because I stood
on the shoulders of giants.  -- Isaac Newton

Roel Schroeven