Data Structures and Algorithms

by Albert Major

1. Strings

Basics (recap)

• A string is a sequence of characters enclosed in single (' ') or double (" ") quotes.
• Strings are immutable – once created, they cannot be changed.

Functions vs Methods

• A function is a standalone operation that takes input and returns output.
• A method is called on an object using a dot (.) notation.
  • Example: a.lower() (method) vs len(a) (function).

Common String Functions

• len(a): Returns the length of the string.
• a.lower(): Converts the string to lowercase.
• a.upper(): Converts the string to uppercase.
• a.strip(): Removes spaces, newlines, and tabs from both ends of the string.
• a.replace("old", "new"): Replaces all occurrences of "old" with "new".

Important Notes on String Methods

• String methods don’t change the original string.

  • Instead, they create and return a new string.

• Example:

  a = "  hello  "
  print(a.strip())  # "hello"
  print(a)  # "  hello  " (Original remains unchanged)