String Operations

String Operations

What it means

Strings in Python are immutable sequences of characters. Every “modification” (like .upper() or .replace()) actually returns a new string rather than changing the original. Python offers a rich set of built-in methods for searching, transforming, splitting, and formatting text.

Examples

name = "  Alice Smith  "

print(name.strip())               # "Alice Smith" -- removes leading/trailing whitespace
print(name.strip().lower())       # "alice smith"
print(name.strip().split(" "))    # ['Alice', 'Smith']
print("-".join(["a", "b", "c"]))  # "a-b-c"
print("world" in "hello world")   # True

age = 30
message = f"Name: {name.strip()}, Age: {age}"   # f-strings for formatting

print("cat" in "concatenate")     # True -- substring check
print("Hello".replace("H", "J"))  # "Jello" -- returns a new string

Common mistake

Assuming string methods modify the string in place — since strings are immutable, you must capture the return value, or the change is silently discarded.

text = "hello"
text.upper()          # does nothing to `text` -- return value is discarded!
print(text)           # still "hello"

text = text.upper()   # correct -- reassign the result
print(text)           # "HELLO"

Quick practice

1. Why doesn’t my_string.upper() change my_string in place?

   Answer

   Strings are immutable in Python — every string method returns a new string rather than mutating the original.

2. What does "a-b-c".split("-") return?

   Answer

   ['a', 'b', 'c']

3. What’s the modern, preferred way to embed variables inside a string?

   Answer

   f-strings — e.g. f"Hello, {name}!" — they're more readable than .format() or %-formatting.