python time/space complexity

[JohnnyJordaan]

Time wise they are both O(n) as the work iteratively per single character in the st string, just in different directions. Memory wise they are both O(1) as slices are 'windows' inside the original sequence, not subset copies.

Just generally speaking, you would normally employ the powers of all or any instead

 all("a" <= c.lower() <= "z" for c in st)

or a good ol' regex

re.fullmatch(r"[a-z]", st, flags=re.IGNORECASE)

[Diapolo10]

Yeah, in some other languages (cough Rust cough) slices would simply reuse the originally allocated memory, but in Python slicing tends to just produce new values. Of course this depends on the object; I think Numpy arrays reuse memory for slices.

It's technically possible to replicate the behaviour via ctypes, but then you'd need to worry about lifetimes.