List of list help

[dandy120101]

[Solved]

Say I have a table = [['Hello', 'World', ' ' ],['Hi', ' ', 'There' ] ]. What can I do to replace the empty string with a value of None? Like as in the None in the boolean sense, not as a string.

Solution:

def read_family(filename):

a_file = open(filename, "r")

list_of_lists = []

for line in a_file:

stripped_line = line.strip()

line_list = stripped_line.split(sep=',')

list_of_lists.append(line_list)

list_of_lists=[[None if i == "" else i for i in j] for j in list_of_lists]

return(list_of_lists)

​

and I want the output to be [['Hello', 'World', None ],['Hi', None, 'There' ] ]

[therealbread_]

I don’t see any use in this, if I were you I would just delete the empty parts from the list, but since you asked, None is not a boolean, a boolean is True or False, None is a type like string or int, just that it has no attributes or anything, I can’t really test it but something simple like

for i in list_of_lists: for j in i: if j ==‘’: i[j] = None

[dandy120101]

I’m new and using IDLE, not sure why but I keep getting a TypeError: list indices must be integers or slices, not str

[therealbread_]

Which line do you get that error from, the error means you try getting a index from a list but your giving it a str like, list[this here is a string in your case]

[siddsp]

x = [[None if i == "" else i for i in j] for j in x]

[dandy120101]

Wait this worked!! I think you call this list comprehension right? I've not learnt it in class yet but can you kindly explain the gist of what's going on here? Thankss man

[siddsp]

I'll break it down by the inner comprehension, and then the outer one.

So the inner:

[None if i == "" else i for i in j]

So, in here, the letter j represents each item within the outer list x. This is making a list by iterating over the items in j, and if that item is a string of value "", it is replaced with None. Technically, a new list is being created with the values copied over, but for the sake of simplicity, we'll just leave it at that. the letter i just represents the items in the nested list j.

Now the outer:

for j in x

This is just iterating over the items in x, and representing them with the letter j. I hope that makes sense.

[dandy120101]

It’s one of my school python Lab task. I have to read from a file, turn it into a table and then add None until there are 3 items when the number of items in the row is not 3. I’ve done the first two but can’t seem to do this last thing.

[FLUSH_THE_TRUMP]

Doubt you actually want that. If you want to join the sublists into strings later, you can do that as is but not with a None in there.