Working with Strings

In Python, a string is a sequence of characters. Unlike numbers, strings are used to represent text. They are created by enclosing characters in single quotes (') or double quotes ("). Python stores strings as a sequence where each character has a specific position called an index.

Python
my_string = 'Hello World'
# Both work the same
another = "Python is fun"

Indexing starts at 0. You can access individual characters using square brackets. Slicing allows you to get a sub-string by specifying a range [start:end]. Negative indices count from the end of the string.

Python
name = "Python"
print(name[0])    # 'P'
print(name[-1])   # 'n' (last char)
print(name[1:4])  # 'yth' (index 1 up to but NOT including 4)

You can combine strings using the plus (+) operator (concatenation) and repeat them using the asterisk (*) operator.

Python
greet = "Hello" + " " + "World"
laugh = "ha" * 3  # "hahaha"

Python provides many built-in methods to transform text. Methods like .upper(), .lower(), .strip() (removes whitespace), and .replace() are commonly used to clean data.

Python
text = "  Python  "
print(text.strip().upper())  # "PYTHON"
print("apple-banana".split("-")) # ['apple', 'banana']

Use the 'in' keyword to check if a substring exists. The .find() method returns the index of the first occurrence, and .count() tell you how many times a substring appears.

Python
msg = "Learning Python is great"
print("Python" in msg)  # True
print(msg.count("e"))    # 2

Modern Python uses f-strings for readability. Just prefix the string with 'f' and use curly braces {} to inject variables directly into the text.

Python
name = "Alex"
score = 95
print(f"User {name} scored {score} points.")

Special characters like newlines (\n) or tabs (\t) use backslashes. If you want backslashes to be treated literally (like in file paths), use a raw string by prefixing it with 'r'.

Python
print("Line 1\nLine 2")
path = r"C:\Users\Documents"

A key rule in Python: Strings are immutable. This means once a string is created, you cannot change its individual characters. Any 'change' actually creates a whole new string in memory.

Python
text = "Python"
# text[0] = 'J'  # This would cause an ERROR
text = "J" + text[1:] # This works (creates new string)

For complex pattern matching (like validating emails), Python uses the 're' module for Regular Expressions. Additionally, computers represent characters using encodings like UTF-8.

Python
import re
# Simple regex example (matches 3 digits)
print(re.findall(r'\d{3}', "Order ID: 123")) # ['123']