python replace None with blank in list using list Comprehensions or something else? Also a nested list solution [duplicate]

Question

a = [None, None, '2014-04-27 17:31:17', None, None]

trying to replace None with ''

tried many times, this the closest I got. b= ['' for x in a if x==None] which gives me four '' but leaves out the date

i thought it would be b= ['' for x in a if x==None else x] but doesn't work.

what if it is nested like so:

a = [[None, None, '2014-04-27 17:31:17', None, None],[None, None, '2014-04-27 17:31:17', None, None],[None, None, '2014-04-27 17:31:17', None, None]]

Can you still use list comprehensions?

Answer 1

Just modify your code as follows:

b = ['' if x is None else x for x in a]    #and use is None instead of == None

>>> print b
['', '', '2014-04-27 17:31:17', '', '']

Explanation

For nested lists, you can do:

b = [['' if x is None else x for x in c] for c in a]

Answer 2

You don't even have to use a comprehension:

a = map(lambda x: '' if x == None else x, a)