String Methods in Practice

Why this matters

Most real data is text: names typed by people, lines from files, web pages. It arrives messy, with extra spaces, odd capitals and punctuation. A handful of string methods clean most of it up.

The idea

Strings cannot be changed, so every method returns a new string (or a list):

raw = "  hello, Python World  "
raw.strip()                 # 'hello, Python World'    (trims both ends)
raw.lower(), raw.upper()
raw.title()                 # '  Hello, Python World  '
raw.replace("l", "L")       # swaps every 'l'
raw.split()                 # ['hello,', 'Python', 'World']  (on whitespace)
"a,b,c".split(",")          # ['a', 'b', 'c']               (on a separator)
"-".join(["a", "b"])        # 'a-b'

Asking questions about text:

"python".startswith("py")   # True
"report.csv".endswith(".csv")   # True
"banana".count("a")         # 3
"banana".find("n")          # 2   (-1 if missing)
"abc".isalpha(), "123".isdigit(), "a1".isalnum()

Remember the pattern from lists: split into pieces, work on each piece, join them back.

Try it

Take " the QUICK brown fox " and produce "The Quick Brown Fox" using split, capitalize and join.

Your turn

Write three functions that return their answers:

clean_name(raw): tidy a typed name. Remove extra spaces and fix capitals: clean_name(" aDA LOVElace ") is "Ada Lovelace".
initials(name): initials("ada lovelace") is "A.L.".
is_palindrome(text): True if the text reads the same backwards, ignoring capitals, spaces and punctuation. "A man, a plan, a canal: Panama" is a palindrome.

Recap

String methods return new strings; the original never changes.
split and join convert between text and lists; strip trims the ends.
Test with startswith, endswith, in, isalpha and isdigit.

Common mistakes

Expecting text.strip() to change text. Assign the result: text = text.strip().
split(" ") vs split(): with an explicit space, repeated spaces produce empty strings.
Using find as a condition: -1 is truthy, and 0 (found at the start) is falsy.