Why does strip() method returns a list from a list of words?

I was trying to make a list with each char of a sentence.

Given the sentence "7h3 qu1ck brown fox jumps ov3r 7h3 lazy dog"

I used the .split() method to separate the words and afterwards another .split() method:

x = [i.split() for i in sentence]

and it returned:

[['7'], ['h'], ['3'], [], ['q'], ['u'], ['1'], ['c'], ['k'], [], ['b'], ['r'], ['o'], ['w'], ['n'], [], ['f'], ['o'], ['x'], [], ['j'], ['u'], ['m'], ['p'], ['s'], [], ['o'], ['v'], ['3'], ['r'], [], ['7'], ['h'], ['3'], [], ['l'], ['a'], ['z'], ['y'], [], ['d'], ['o'], ['g']]

So I was trying to figure out why this was happening and tried with:

[i.strip() for i in sentence if len(i) > 0]

and it returned:

['7', 'h', '3', '', 'q', 'u', '1', 'c', 'k', '', 'b', 'r', 'o', 'w', 'n', '', 'f', 'o', 'x', '', 'j', 'u', 'm', 'p', 's', '', 'o', 'v', '3', 'r', '', '7', 'h', '3', '', 'l', 'a', 'z', 'y', '', 'd', 'o', 'g']

1. The first issue I'm facing is that I don't know why is returning empty strings.

2. The second issue is that I don't know why strip() behaves differently than .split(). I think that maybe it can be related to the return statement of each method, but I would like to understand better why this happen.

.split(delim) takes in a string and returns a list of substrings that are between delim. .strip() will remove any leading or trailing whitespace from the string and return the resulting string.

The first issue you encountered was that you were splitting the string incorrectly. In x = [i.split() for i in sentence], you iterate over every character of sentence, not every word. So, i.split() is attempting to split a single character by nothing. This doesn't make much sense, so it just returns a list with that character. See this below:

>>> sentence = '7h3 qu1ck brown fox jumps ov3r 7h3 lazy dog'
>>> [i for i in sentence]
['7', 'h', '3', ' ', 'q', 'u', '1', 'c', 'k', ' ', 'b', 'r', 'o', 'w', 'n', ' ', 'f', 'o', 'x', ' ', 'j', 'u', 'm', 'p', 's', ' ', 'o', 'v', '3', 'r', ' ', '7', 'h', '3', ' ', 'l', 'a', 'z', 'y', ' ', 'd', 'o', 'g']
>>> sentence.split(' ')
['7h3', 'qu1ck', 'brown', 'fox', 'jumps', 'ov3r', '7h3', 'lazy', 'dog']

Instead, you want to split by each space character (' ') to get a list of each word:

x = sentence.split(' ')

In response to what you were trying to do:
> I was trying to make a list with each char of a sentence.

All you need to do is convert the string to a list with list(). For example:

>>> list('7h3 qu1ck brown fox jumps ov3r 7h3 lazy dog')
['7', 'h', '3', ' ', 'q', 'u', '1', 'c', 'k', ' ', 'b', 'r', 'o', 'w', 'n', ' ', 'f', 'o', 'x', ' ', 'j', 'u', 'm', 'p', 's', ' ', 'o', 'v', '3', 'r', ' ', '7', 'h', '3', ' ', 'l', 'a', 'z', 'y', ' ', 'd', 'o', 'g']

If you first want to split by each word, then get each character of of each word, then do this:

>>> [list(word) for word in '7h3 qu1ck brown fox jumps ov3r 7h3 lazy dog'.split()]
[['7', 'h', '3'], ['q', 'u', '1', 'c', 'k'], ['b', 'r', 'o', 'w', 'n'], ['f', 'o', 'x'], ['j', 'u', 'm', 'p', 's'], ['o', 'v', '3', 'r'], ['7', 'h', '3'], ['l', 'a', 'z', 'y'], ['d', 'o', 'g']]