CLASS WITH CARREIRO

len(s): Returns the length of string s.
```
len("hello")  # Output: 5
```

s.lower(): Converts all characters in s to lowercase.
```
"Hello".lower()  # Output: "hello"
```
s.upper(): Converts all characters in s to uppercase.
```
"Hello".upper()  # Output: "HELLO"
```
s.capitalize(): Capitalizes the first letter in s.
```
"hello".capitalize()  # Output: "Hello"
```
s.title(): Capitalizes the first letter of each word in s.
```
"hello world".title()  # Output: "Hello World"
```

s.find(sub): Returns the index of the first occurrence of sub in s (or -1 if not found).
```
"hello".find("e")  # Output: 1
```
s.count(sub): Counts the occurrences of sub in s.
```
"banana".count("a")  # Output: 3
```
s.startswith(prefix): Checks if s starts with prefix.
```
"hello".startswith("he")  # Output: True
```
s.endswith(suffix): Checks if s ends with suffix.
```
"hello".endswith("lo")  # Output: True
```

s.strip(): Removes whitespace from both ends of s.
```
" hello ".strip()  # Output: "hello"
```
s.replace(old, new): Replaces all occurrences of old with new in s.
```
"hello".replace("e", "a")  # Output: "hallo"
```
s.split(separator): Splits s into a list using separator (default is whitespace).
```
"a,b,c".split(",")  # Output: ["a", "b", "c"]
```
separator.join(iterable): Joins elements of iterable with separator between each element.
```
"-".join(["a", "b", "c"])  # Output: "a-b-c"
```

s.isalpha(): Checks if all characters in s are alphabetic.
```
"hello".isalpha()  # Output: True
```
s.isdigit(): Checks if all characters in s are digits.
```
"123".isdigit()  # Output: True
```
s.isalnum(): Checks if all characters in s are alphanumeric.
```
"hello123".isalnum()  # Output: True
```
s.swapcase(): Swaps uppercase to lowercase and vice versa.
```
"Hello".swapcase()  # Output: "hELLO"
```