Lesson 32/48 · 📦 Data Structures
📦 Data StructuresLesson 32/48
Phase 5 · Data Structures20 min

String Methods

len, upper, lower, split, join, replace, the toolkit for text

Strings have built-in methods, actions you can call on them using dot notation. You've already used print(); now meet the toolkit for text manipulation.
Calling a method with dot notationpython
name = "alice"
print(name.upper())   # ALICE
print(name.lower())   # alice, original is unchanged
print(len(name))      # 5  (len is a function, not a method)
Methods don't change the original string, they return a new one. Strings in Python are *immutable*.
The most useful string methods
  • s.upper() / s.lower(), change case
  • s.strip(), remove leading/trailing whitespace (great for cleaning user input)
  • s.replace(old, new), swap one substring for another
  • s.split(sep), split into a list of parts
  • sep.join(list), join a list back into a string
  • s.startswith(x) / s.endswith(x), boolean checks
    • strip and replacepython
    raw = "  Hello, World!  "
clean = raw.strip()
print(clean)                   # Hello, World!
print(clean.replace("World", "Python"))  # Hello, Python!
    🤔Quick Check

    What does "hello".upper() return?

    split and join, a power duopython
    sentence = "one,two,three"
words = sentence.split(",")    # ["one", "two", "three"]
print(words[1])                # two

rejoined = " - ".join(words)   # "one - two - three"
print(rejoined)
    split() with no argument splits on any whitespace (spaces, tabs, newlines) and removes the empty strings, handy for tokenising sentences.
    The `in` operator, check if a substring exists
    You already know in for loops. With strings it tests membership:
    in operator for stringspython
    email = "alice@example.com"
if "@" in email:
    print("Looks like a valid email")

print("@" in email)    # True
print("xyz" in email)  # False
    🤔Quick Check

    What does "apple,banana,cherry".split(",") produce?

    Practice Exercises

    0/3 solved
    Exercise 1 of 3easy
    ⏱ 00:00

    Name Formatter

    Write a program that takes a name with messy casing and extra spaces and prints it in "Title Case" with no leading/trailing whitespace.
    Input (already in the code): " alice SMITH "Expected output: Alice Smith
    Hint: chain .strip() then .title()
    solution.py
    1 / 3
    Exercise 2 of 3easy
    ⏱ 00:00

    CSV Row Parser

    You receive a line from a CSV file: "Alice,30,London"
    Split it into parts and print:- Name: Alice- Age: 30- City: London
    solution.py
    2 / 3
    Exercise 3 of 3medium
    ⏱ 00:00

    Censor Filter

    Replace every occurrence of the word "bad" in a message with "***", then check if the cleaned message still contains "bad".
    Message: "This is bad and really bad behaviour"
    Print the cleaned message, then print True or False for whether "bad" is still in it.
    solution.py
    3 / 3
    Solve all 3 exercises to unlock completion
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