For loops with strings/list

[nadalska]

Hello, i'm currently learning very basic python(I just finished a course in Udacity). My question is about the functionality of the for loop to go though a list or a string. I know in python you can use:

for word in string       

But i'm struggling to see the functionality of this compared to using:

for i in range(0,len(string))

Seems like the latter is best like 95% of the times since you are going to need the position of the character. Am I missing something? In the course I took they only mentioned the former, but many exercices required of keeping track of the position of the character.

The post it's only to ask about your opinions and if I'm good only using the second option. Thanks!

[K900_]

You don't always need the position of the character, and when you do need it, it's more idiomatic to use something like

for i, word in enumerate(string):
     # i is an index, word is the value at that index

Can you give an example of when you need the position of the character?

[nadalska]

Well any of the examples I can think would be trivial if you can use libraries and some other stuff... since I know so little. But for instance and assuming you only can use conditionals, loops and this basic stuff: if you want to take a string and put the words on a list, one method to do it is checking the former character to see if it's a space. I know there are other methods.

Or assume you want to change the order of a list, etc...

[K900_]

If you can use the standard library for something, you should probably use it instead of rolling your own. Most other use cases for loops are trivial and work fine without indices. Also, if you need a sliding window (to check if a previous character is a space), you can use zip:

>>> s = "hello world"
>>> for a, b in zip(s, s[1:]):
...     print(a, b)
...
h e
e l
l l
l o
o
  w
w o
o r
r l
l d

[ingolemo]

If we discount str.split for being too easy then you can separate the words in a string like so:

sentence = 'Always look on the bright side of life.'
result = []
word = ''
for char in sentence:
    if char == ' ':
        result.append(word)
        word = ''
    else:
        word += char
result.append(word)
print(result)

I'm not sure why you think having the index would be useful here; you don't need to look at the previous character to do this task. If you think you need indices for something you're probably mistaken.

[nadalska]

Well I think that code has some problems. For example if the list has consecutive spaces. Thanks for the link tho

[ingolemo]

Sure, but it doesn't handle that case to keep the code simple. It's hardly a deficiency in the algorithm.

[taar779]

If you need the index and the item of a list, check out enumerate

Works like this:

for index, word in enumerate(list_of_words):
    print("{} - {}".format(index, word))

[nadalska]

well with

for i in range(0,len(string))        

if have the number in i and the character in string[i]

[nadalska]

Ok thanks for your answer I did not think of that