Count letter occurrences in a case insensitive sentence

Question

I wanted to be able to leave the variables of input as lower/upper to count equivalent letters in the sentence.

Only the variable is as iterable, and when I add the .lower() she changes to str and the code no longer works. I wanted help to do this another way.

Follows the code:

frase = input('Digite uma frase: ')
letra = input('Qual letra você deseja escanear? ')
c = 0
pos = []
for x in frase:
    if x == letra:
        c += 1
for n in enumerate(frase):
    if letra == n[1]:
        pos.append(n[0])
if c != 0:
    print(f'Existem {c} letra(s) "{letra}" na frase, nas posições {pos}.')
else:
    print(f'Não existe nenhum "{letra}" nesta frase.')

Answer 1

You can only use upper and lower in the comparison letter and use a single for to add the position and compare according to the following code:

frase = input('Digite uma frase: ')
letra = input('Qual letra você deseja escanear? ')
c = 0
pos = []

for x in range(len(frase)):
    if frase[x] == letra.lower() or frase[x] == letra.upper():
        pos.append(x+1)
        c += 1

if c != 0:
    print(f'Existem {c} letra(s) "{letra}" na frase, nas posições {pos}.')
else:
    print(f'Não existe nenhum "{letra}" nesta frase.')

By doing this you avoid modifying your "phrase" variable and prevent it from changing its type.

Answer 2

I couldn’t understand what you meant by "when I add the .lower() she changes to str and the code no longer works", but anyway, if you want to capitalize everything (or everything in capital letters) in order to be able to make comparisons, one option would be to make input:

# transforma tudo em maiúscula
frase = input('Digite uma frase: ').upper()
letra = input('Qual letra você deseja escanear? ').upper()

# ou transforma tudo em minúscula
frase = input('Digite uma frase: ').lower()
letra = input('Qual letra você deseja escanear? ').lower()

Another detail is that you don’t have to do two loops. The enumerate already returns at the same time the position and the respective character, so just do:

c = 0
pos = []
for posicao, caractere in enumerate(frase):
    if letra == caractere:
        pos.append(posicao)
        c += 1

Or you can store only the list of positions, without needing the counter. If at the end of the for the list is empty, it is because it did not find anything:

pos = []
for posicao, caractere in enumerate(frase):
    if letra == caractere:
        pos.append(posicao)
if pos:
    print(f'Existem {len(pos)} letra(s) "{letra}" na frase, nas posições {pos}.')
else:
    print(f'Não existe nenhum "{letra}" nesta frase.')

The if pos: check if the list is not empty (here is used the fact that empty lists are considered False). Then, to know how many times the letter occurs, just get the list size with len.

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You can still change the for above by a comprehensilist on, much more succinct and pythonic.:

pos = [ posicao for posicao, caractere in enumerate(frase) if letra == caractere ]

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Of course you could also leave the sentence intact and only convert it to uppercase (or lowercase) when comparing the characters:

frase = input('Digite uma frase: ')
letra = input('Qual letra você deseja escanear? ').lower()

pos = [ posicao for posicao, caractere in enumerate(frase) if letra == caractere.lower() ]

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Finally, if you really want to make a comparison case insensitive, can use the method casefold. It is similar to lower(), but a little more "aggressive" and treats special cases, as for example the character ß, which, when converted to capital, becomes "SS" (then 'ß'.upper().lower() returns "ss"):

print('ß'.lower() == 'SS'.lower()) # False
print('ß'.casefold() == 'SS'.casefold()) # True

Of course, for texts in Portuguese, it won’t make that much difference to use lower() or casefold(), but anyway, the tip is recorded.