change some lowercase letters to uppercase in string

Question

index = [0, 2, 5]
s = "I am like stackoverflow-python"
for i in index:
        s = s[i].upper()
print(s)

IndexError: string index out of range

I understand that in the first iteration the string, s, become just the first character, an uppercase "I" in this particular case. But, I have tried to do it without the "s = " , using swapchcase() instead, but it's not working.

Basically, I'm trying to print the s string with the index letters as uppercase using Python 3.X

Solution 1

Strings are immutable in Python, so you need to create a new string object. One way to do it:

indices = set([0, 7, 12, 25])
s = "i like stackoverflow and python"
print("".join(c.upper() if i in indices else c for i, c in enumerate(s)))

printing

I like StackOverflow and Python

Solution 2

Here is my solution. It doesn't iterate over every character, but I'm not sure if converting the string to a list and back to a string is any more efficient.

>>> indexes = set((0, 7, 12, 25))
>>> chars = list('i like stackoverflow and python')
>>> for i in indexes:
...     chars[i] = chars[i].upper()
... 
>>> string = ''.join(chars)
>>> string
'I like StackOverflow and Python'

Comments

[jfs]

you don't need set() in this case. string = list(..) is misleading, you could use chars (less misleading).

[Tyler Crompton]

True. I actually optimized the solution and converting to a list is no longer needed. Thanks, though. :)

[Tyler Crompton]

And yes, using set is unnecessary but what if the OP want to add an index? A set would make sense for this purpose.

[jfs]

1. from MutableString docstring: A faster and better solution is to rewrite your program using lists. 2. indexes = [0, 2, 5] ... OP want to add an index ... indexes.append(1).

[Tyler Crompton]

But if an index already exists, you're doubling the work for that index. It just makes sense to use a set. From set's docstring: "Build an unordered collection of unique elements." It doesn't need to be ordered and every index should be unique since it wouldn't make sense to have duplicates.

[Tyler Crompton]

Rolled back. I found some benchmarking and this looks to be quickest.

[jfs]

imagine you use .swapcase() instead of .upper() then list() and set() indexes yield different results. btw, string = ''.join(string) looks awkward string = ''.join(chars) might be better in this case.

[Tyler Crompton]

Why use swapcase() when you're specifying the indexes to be capitalized? Why would you add an index a second time to practically remove it? It's semantically incorrect and set is the proper data structure. As far as changing, the name of the variable, done. Thanks. :)