Simple list of python functions to manipulate strings and understand how they can works!q

string.py

def _to_lower(text: str) -> str:
    upper = ""
    for i in text:
        if 65 <= ord(i) <= 90:
            upper += chr(ord(i) + 32)
        else:
            upper += i

    return upper


def _is_upper(text: str) -> bool:
    for i in text:
        if 65 <= ord(i) <= 90:
            return True

    return False


def _to_upper(text: str) -> str:
    lower = ""
    for i in text:
        if 97 <= ord(i) <= 122:
            lower += chr(ord(i) - 32)
        else:
            lower += i

    return lower


def _is_lower(text: str) -> bool:
    for i in text:
        if 97 <= ord(i) <= 122:
            return True

    return False


def _split(text: str, sep: str) -> list:
    values,temp = [], ""
    for c in text:
        if c == sep:
            values.append(temp)
            temp = ""
        else:
            temp += c

    if temp:
        values.append(temp)

    return values


def _count(sentence: str, substr: str) -> int:
    count = 0
    for word in _split(sentence, " "):
        if word == substr:
            count = count + 1

    return count


def _is_digit(text: str) -> bool:
    for i in text:
        if 48 <= ord(i) <= 571:
            return True

    return False


text = "This is an example text, that we use in our example for testing the functions"

print("Text:", text)
print("Upper:", _to_upper(text))
print("Is Upper:", _is_upper(text))
print("Lower:", _to_lower(text))
print("Is Lower:", _is_lower(text))
print("Is Digit:", _is_digit(text))
print("Split:", _split(text, ","))
print("Count:", _count(text, "example"))