Iterating over strings in python

Question

>>> bob = "bob"
>>> range(0, len(bob))
[0, 1, 2]
>>> bob[0:2]
'bo'
>>> bob[0:3]
'bob'

Is there a convenient way to iterate over strings in python when I need the index number? If I make a for loop with range(0, len(astring)), it will only end up going up to the second-to-last character: I would instead have to write range(0, len(astring) + 1), which is kind of annoying. I can't do for c in astring because I am taking substrings. Suggestions?

I suppose you could always write a wrapper function to replace len such that it returns the result of len but with 1 added to it. — BlackVegetable
– BlackVegetable, Commented Feb 8, 2014 at 21:22
@BrenBarn There's good reason to have separate notations for inclusive and exclusive bounds. For example, [x, y] vs [x, y) in mathematics, and x to y vs x until y in the scala core library. It's a more direct expression of your intention. — Chris Martin
– Chris Martin, Commented Feb 8, 2014 at 21:45

roippi · Accepted Answer · 2014-02-08 21:38:15Z

3

Use enumerate:

for i,c in enumerate('bob'):
    print('{}: {}'.format(c,i))

b: 0
o: 1
b: 2

Your bit about "substrings" is a bit under-specified, but chances are slicing will do what you need:

s = 'banana'

for i,c in enumerate(s):
    print(s[i:])

banana
anana
nana
ana
na
a

notably, you can leave off either the start or end bound to a slice (or both!) and the slice will just go all the way up to that end.

edited Feb 8, 2014 at 21:38

answered Feb 8, 2014 at 21:23

roippi

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2 Comments

DSM Over a year ago

I got the impression the OP wanted to loop over substrings, not characters.

roippi Over a year ago

@DSM well then just replace 'bob' with bob's substring, no?

dawg · Accepted Answer · 2014-02-08 21:41:48Z

1

Suppose you have:

>>> st='a string with substrings'

Of course it is easy to just split that:

>>> st.split()
['a', 'string', 'with', 'substrings']

But suppose you want to deal with indices of the string based on some condition.

You can define the indices that you want (trivially by spaces here, but could be some other condition):

>>> sub_strings=[0]+[i+1 for i, c in enumerate(st) if c.isspace()]+[len(st)]

Then you can use slice like so:

>>> for t in zip(sub_strings, sub_strings[1:]):
...    print st[slice(*t)], t
... 
a  (0, 2)
string  (2, 9)
with  (9, 14)
substrings (14, 24)

answered Feb 8, 2014 at 21:41

dawg

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