pythonlistlist-manipulation

Some built-in to pad a list in python

I have a list of size < N and I want to pad it up to the size N with a value.

Certainly, I can use something like the following, but I feel that there should be something I missed:

>>> N = 5
>>> a = [1]
>>> map(lambda x, y: y if x is None else x, a, ['']*N)
[1, '', '', '', '']
Solution 
  • a += [''] * (N - len(a))

    or if you don't want to change a in place

    new_a = a + [''] * (N - len(a))

    you can always create a subclass of list and call the method whatever you please

    class MyList(list):
    def ljust(self, n, fillvalue=''):
        return self + [fillvalue] * (n - len(self))

a = MyList(['1'])
b = a.ljust(5, '')