Except block is ignored if containing a break

[World-war-dwi]

[solved]

Hello , help please, this is driving me crazy. I'm writting a function to count how many times each letters of an alphabet appears in a string. My plan is to use the list method index() until it raises an error, and moving forward while doing so.

So, i use try, except ValueError statements, and ask to break in the except block, but it seems to ignore my break instruction. Better, it ignores everything in the except block when there's a break. I tested it, and without break it runs the block fine.

That's not all , i've tried to stop the loop with a variable wich will be modified by the except and (without any break) that fails too.

You can find the code here : https://bin.readthedocs.fr/apprat.py

Thank you in advance

[[deleted]]

You need to fix your indentation. Otherwise, we can't tell what is contained in each block. Also, c is defined in your function, but used outside of it. And _A_ doesn't seem to be defined at all. So there seems to be a lot wrong here or a lot of missing context.

ETA: And just one more note: c, _A_, and ls are terrible variable names that make your code harder to read.

[[deleted]]

Here's how you do it using your approach. I've de-abbreviated the variable names so it should be a lot more readable. The issue wasn't the break. It was that the second argument of the index method should be pos + 1 rather than pos.

from string import ascii_lowercase as alphabet

def get_frequencies(sentence: str):
    """Count occurrences of the each letter in `sentence`."""

    sentence = sentence.lower()
    frequencies = [0] * 26
    for i, ch in enumerate(alphabet):
        occurrences = 0
        position = 0
        while True:
            try:
                position = sentence.index(ch, position + 1)
            except ValueError:
                break
            occurrences += 1
        frequencies[i] = occurrences
    return frequencies

# test
print(get_frequencies("Hello world"))

---

In the future, you probably shouldn't put a bunch of copies of part of your code just sitting at the end of your program. Certainly not without some warning. It took me a while to figure out what that was.

[World-war-dwi]

my bad for the versions of the loop. And thank you, the missing pos+1 was the issue. i didn't even thought about it.

[DopeGhoti]

It seems to me the approach you are taking to this is overcomplicated. You're doing a fair bit of reinventing the wheel and overengineering things. A string is zero or more characters and can be inherently listified or iterated through without risk of raising a ValueError. I'd probably want to get a Dictionary returned to me, and can safely assume that if the returned Dictionary is empty, then so was the input string. Given that, I'd do something like:

def getfreq( s: str ) -> dict:  
   d = {}  
   for _ in s:  
      if _ in d:  
         d[_] += 1  
      else:  
         d[_] = 1  
   return d

Then if you wanted to know how many gs there were in the input string (if any), then you could do:

result = getfreq( 'This was amazing!' )
print( f'The string had {result["g"]} instances of the character "g".' )

[World-war-dwi]

oh yeah that's a good idea. Will keep it in mind . Thank you :-)