How to break up a string in python without using the split function

Question

I am trying to break a sentence up into words and then print each word on a separate line. But I am not allowed to use the split function. It should be done using lists and such. So far I have:

text=input("Enter text:")+''
L=len(text)
i=0
while i!=L:
    bi=i
    while text[i]!='':
        i=i+1
        print(text[bi:i])
        i=i+1

But this results in the sentence being broken up letter by letter:

i.e.

"Hello."

becomes:

H
He
Hel
Hell
Hello

Also, what I have now leaves off the last character. And I get the error message:

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    while text[i]!='':
IndexError: string index out of range

What does this message mean?

Answer 1

As I commented your indexing is incorrect, both loops would need to be to the length of the text -1 while i < L, also adding an empty string does not do what you think, text[i] will never be equal to '':

In [1]: text = input("Enter text:") + ''  
Enter text:foo

In [2]: len(text) # still length 3
Out[2]: 3

In [4]: len("")
Out[4]: 0

But a simpler method if your words are delimited by whitespace is to use a for loop, when you encounter whitespace print the chars you have to that point and reset a tmp variable:

text=input("Enter text:")
tmp = ""
for ch in text:
    # if ch is whitespace and we have some chars
    if ch.isspace() and tmp:
        print(tmp)
        tmp = ""
    else:
        tmp += ch
# catch last word
if tmp:
     print(tmp)

Answer 2

You are getting your error because Python is zero indexed:

test_string = "abc"
print(len(test_string)) # prints 3

foo = test_string[3] # causes error because characters are at indexes 0 - 2
                     # 3 is out of range

You can side step the issue of mismatched indexes by not even using them. Whenever possible, let Python manage the indexes by using a for loop to iterate over a list or string:

s = "this is a string that I want to split"

words = [] # create an empty list of your words
chars = [] # create an empty list of characters

for char in s:

    if char == " " and chars: # if the character is a space and we've stored some chars
        words.append("".join(chars)) # combine the stored chars into a word and add it to 
                                     # the word lise
        chars = [] # clear out the stored chars

    elif char != " ":
        chars.append(char) # otherwise, store the char if it's not a space

if chars:
    words.append("".join(chars)) # add the last word found to the word list

Note that by using the for loop, you don't have to manually manage any indexes.

Answer 3

You could try regex if using lists is not a hard requirement. This regex breaks a string up into words and returns a list containing the words.

(\S+)\s*

Regex101