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how to split a list every nth item

I am trying to split a list every 5th item, then delete the next two items ('nan'). I have attempted to use List[:5], but that does not seem to work in a loop. The desired output is: [['1','2','3','4','5'],['1','2','3','4','5'],['1','2','3','4','5'],['1','2','3','4','5']]
List = ['1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan']
for i in List:
# split first 5 items
# delete next two items
# Desired output:
# [['1','2','3','4','5'],['1','2','3','4','5'],['1','2','3','4','5'],['1','2','3','4','5']]

There are lots of ways to do this. I recommend stepping by 7 then splicing by 5.
data = ['1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan']
# Step by 7 and keep the first 5
chunks = [data[i:i+5] for i in range(0, len(data), 7)]
print(*chunks, sep='\n')
Output:
['1', '2', '3', '4', '5']
['1', '2', '3', '4', '5']
['1', '2', '3', '4', '5']
['1', '2', '3', '4', '5']
Reference: Split a python list into other “sublists”...

WARNING: make sure the list follows the rules as you said, after every 5 items 2 nan.
This loop will add the first 5 items as a list, and delete the first 7 items.
lst = ['1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan']
output = []
while True:
if len(lst) <= 0:
break
output.append(lst[:5])
del lst[:7]
print(output) # [['1', '2', '3', '4', '5'], ['1', '2', '3', '4', '5'], ['1', '2', '3', '4', '5'], ['1', '2', '3', '4', '5']]

List=['1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan']
new_list = list()
for k in range(len(List)//7):
new_list.append(List[k*7:k*7+5])
new_list.append(List[-len(List)%7])

Straightforward solution in case if the list doesn’t follow the rules you mentioned but you want to split sequence always between NAN's:
result, temp = [], []
for item in lst:
if item != 'nan':
temp.append(item)
elif temp:
result.append(list(temp))
temp = []

Using itertools.groupby would also support chunks of different lengths:
[list(v) for k, v in groupby(List, key='nan'.__ne__) if k]

I guess there is more pythonic way to do the same but:
result = []
while (len(List) > 5):
result.append(List[0:0+5])
del List[0:0+5]
del List[0:2]
This results: [['1', '2', '3', '4', '5'], ['1', '2', '3', '4', '5'], ['1', '2', '3', '4', '5'], ['1', '2', '3', '4', '5']]

mainlist=[]
sublist=[]
count=0
for i in List:
if i!="nan" :
if count==4:
# delete next two items
mainlist.append(sublist)
count=0
sublist=[]
else:
# split first 5 items
sublist.append(i)
count+=1

Generally numpy.split(...) will do any kind of custom splitting for you. Some reference:
https://docs.scipy.org/doc/numpy/reference/generated/numpy.split.html
And the code:
import numpy as np
lst = ['1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan','1','2','3','4','5','nan','nan']
ind=np.ravel([[i*7+5, (i+1)*7] for i in range(len(lst)//7)])
lst2=np.split(lst, ind)[:-1:2]
print(lst2)
Outputs:
[array(['1', '2', '3', '4', '5'], dtype='<U3'), array(['1', '2', '3', '4', '5'], dtype='<U3'), array(['1', '2', '3', '4', '5'], dtype='<U3'), array(['1', '2', '3', '4', '5'], dtype='<U3')]

I like the splice answers.
Here is my 2 cents.
# changed var name away from var type
myList = ['1','2','3','4','5','nan','nan','1','2','3','4','10','nan','nan','1','2','3','4','15','nan','nan','1','2','3','4','20','nan','nan']
newList = [] # declare new list of lists to create
addItem = [] # declare temp list
myIndex = 0 # declare temp counting variable
for i in myList:
myIndex +=1
if myIndex==6:
nothing = 0 #do nothing
elif myIndex==7: #add sub list to new list and reset variables
if len(addItem)>0:
newList.append(list(addItem))
addItem=[]
myIndex = 0
else:
addItem.append(i)
#output
print(newList)

Convert List of string to Integer

I have a list whose elements are only single string.
my_list = ['9', '4', '4', '5', '4', '3', '5']
How can I convert this into a single integer like: 9445435
Note: ' '.join() only works for lists of strings, not integers.

Try this,
In [5]: int(''.join(my_list))
Out[5]: 9445435

Why don't you try this approach?
my_list = ['9', '4', '4', '5', '4', '3', '5']
output = int(''.join(str(num) for num in my_list))
print(output) ## 9445435

result = ' '.join(my_list)
result = int(result)

How to create lists in list where every future list is separate by spaces in list

User provides input with spaces:
row = list(input())
print(row)
['1','2','3',' ','4','5','6',' ','7','8','9',' ']
So I need to create 'row' list into the below. The list is divided into sub-lists based on whitespace:
[['1','2','3'],['4','5','6'],['7','8','9']]

You can use str.split to split by whitespace:
myinput = '123 456 789'
row = list(map(list, myinput.split()))
print(row)
[['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]
Alternatively, using a list comprehension:
row = [list(i) for i in myinput.split()]

You can usestr.split to split the input on spaces to give a list of sub-strings.
E.g. '123 456 789' would become ['123', '456', '789'].
Then use a list-comprehension to convert these strings into lists of characters with the list() constructor (as you are already familiar with).
Making the final code:
row = [list(s) for s in input().split()]
#[['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]

Starting with your list rather than the string, you can do that using itetools.groupby:
from itertools import groupby
row = ['1','2','3',' ','4','5','6',' ','7','8','9',' ']
out = [list(group) for key, group in groupby(row, lambda x: x != ' ') if key]
print(out)
# [['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]
We group the values depending on whether or not they are spaces, and only keep the groups that are not made of spaces.

Try this:
abc=['1','2','3',' ','4','5','6',' ','7','8','9',' ']
newList=list()
temp=list()
for i in abc:
if(i==' '):
newList.append(temp)
temp=list()
else:
temp.append(i)
print(newList)
Output:
[['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]

How to turn a list of integers into a string of numbers?

I'd like to turn
[1,2,3,4,5,4,3,2,1]
into
['1','2','3','4','5','4','3','2','1']
in preparation of doing FreqDist.

Use the built-in map function when casting each item in the list:
newList = map(str, oldList)

Just use a simple list comprehension
>>> myar=[1,2,3,4,5,4,3,2,1]
>>> [str(i) for i in myar]
['1', '2', '3', '4', '5', '4', '3', '2', '1']

How to split string array to 2-dimension char array in python

I have a string array, for example:
a = ['123', '456', '789']
I want to split it to form a 2-dimension char array:
b = [['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]
I'm using
[[element for element in line] for line in array]
to achieve my goal but found it not easy to read, is there any built-in function or any readable way to do it?

Looks like a job for map:
>>> a = ['123', '456', '789']
>>> map(list, a)
[['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]
Relevant documentation:
map
list

you could do something like:
first_list = ['123', '456', '789']
other_weirder_list = [list(line) for line in first_list]
Your solution isn't that bad, but you might do something like this or the map suggestion by arashajii.

map(list, array) should do it.

You can use map:
>>> a
['123', '456', '789']
>>> map(list, a)
[['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]
Although I really don't see why you'd need to do this (unless you plan on editing one specific character in the string?). Strings behave similarly to lists.

First I tried e.split(''), but I get ValueError: empty separator.
Try this:
a = ['123', '456', '789']
b = [list(e) for e in a]
b
[['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]