Python - String Methods

Overview

Estimated time: 25–40 minutes

This page is a practical reference of common string methods with concise examples, expected output, and notes on behavior and pitfalls.

Learning Objectives

• Recall and apply core string methods (split, join, replace, find, startswith, endswith, strip, case conversions, etc.).
• Understand when to choose methods vs slicing or regex.
• Avoid common Unicode and whitespace pitfalls.

Examples

s = "  Hello, World!  "
print(s.strip())         # remove outer whitespace
print(s.lower())         # lowercase
print("hi,there".split(","))
print(", ".join(["a","b","c"]))
print("banana".replace("na","NA"))

Expected Output:

Hello, World!
hello, world!
['hi', 'there']
a, b, c
baNANA

Guidance & Patterns

• Show partition/rpartition vs split when you need exactly 3 parts.
• Explain find/rfind (return -1) vs index/rindex (raise ValueError).
• Demonstrate startswith/endswith with tuples for multiple prefixes/suffixes.

Best Practices

• Unicode: normalization (NFC/NFD) can affect comparisons; consider unicodedata.normalize for canonical forms.
• Performance: prefer chaining simple methods over regex for trivial cases; measure with timeit.

Method Walkthrough

• split(sep=None, maxsplit=-1), rsplit
• join(iterable)
• strip, lstrip, rstrip
• replace(old, new, count=-1)
• find/rfind, index/rindex
• startswith/endswith
• count
• capitalize, title, upper, lower, casefold
• removeprefix, removesuffix (3.9+)

Checks for Understanding

1. How do you split only on the first dash in "a-b-c"?
2. What’s the difference between find and index?