how to fill a list with 0 using python

I want to get a fixed length list from another list like:

a = ['a','b','c']
b = [0,0,0,0,0,0,0,0,0,0]

And I want to get a list like this: ['a','b','c',0,0,0,0,0,0,0]. In other words, if len(a) < len(b), i want to fill up list a with values from list b up to length of the list b, somewhat similar to what str.ljust does.

This is my code:

a=['a','b','c']
b = [0 for i in range(5)]
b = [a[i] for i in b if a[i] else i]

print a

But it shows error:

  File "c.py", line 7
    b = [a[i] for i in b if a[i] else i]
                                    ^
SyntaxError: invalid syntax

What can i do?