I've been struggling for a while with this. I have a list with sublist and I wanted to add an element that is a space before each element of the sublists. for example:
lin = [[2], [3], [2], [2, 2], [2]]
the result should be:
lin = [[' ',2], [' ',3], [' ',2], [' ',2, ' ',2], [' ',2]]
I've tried to do this:
for a in lin:
for e in a:
e = (' ') , e
but I obtained exactly the same list with no alterations
I assume that you actually meant something like the comment of Tigerhawk.
Your problem is that e= (' ') , e is just overwriting the value of e (which was originally each value in your nested list) to a tuple containing a space and the original value. This doesnt actually change anything inside of your list, just changes whatever it is that e was originally pointing to.
You can instead do something like this:
>>> lin = [[2], [3], [2], [2, 2], [2]]
>>> for a in lin:
for i in range(len(a)-1,-1,-1):
a.insert(i, ' ')
>>> lin
[[' ', 2], [' ', 3], [' ', 2], [' ', 2, ' ', 2], [' ', 2]]
Note the inner loop: for i in range(len(a)-1,-1,-1): This is done this way because of 2 reasons:
a since you are going to be changin the values in a
[2, 2] element in there. Good work Stomach Whisperer
You can use list comprehension and chain.from_iterable from itertools
>>> from itertools import chain
>>> lin = [[2], [3], [2], [2, 2], [2]]
>>> [list(chain.from_iterable([(' ', i) for i in j])) for j in lin]
[[' ', 2], [' ', 3], [' ', 2], [' ', 2, ' ', 2], [' ', 2]]
>>>
A neat, functional solution, that uses only built-in functions
lin = [[2], [3], [2], [2, 2], [2]]
add_spaces = lambda l: [i for x in zip(' '*len(l), l) for i in x]
new_list = [add_spaces(l) for l in lin]
Output:
>>> print new_list
[[' ', 2], [' ', 3], [' ', 2], [' ', 2, ' ', 2], [' ', 2]]
lambda l: list(itertools.chain.from_iterable(zip(itertools.repeat(' '), l)))
lin=[[' ',2], [' ',3], [' ',2], [' ',2, ' ',2], [' ',2]]?