String Handling Overview

What you will learn

Topic	Goal
Indexing & Slicing	Access one or many characters visually
Immutability	Why characters cannot be modified directly
String Methods	Learn the important built-in str methods
Method Flow	Understand how methods return new strings

For string basics (quotes, creation, sequence type), see str — String Data Type. This lesson sets up the method work in the rest of the module.

1. Strings are sequences

A string is a sequence of characters. Think of each character as living inside its own numbered box.

s = "python"

Memory trick: Every character has its own locker number (index).

2. Indexing → Get one character

Indexing always returns one character.

s = "python"

print(s[0])   # p
print(s[5])   # n

3. Slicing → Get multiple characters

Slicing returns a range of characters.

s = "python"

print(s[1:4])   # yth

Easy memory: Start ✔ | Stop ✗

4. Why strings are immutable

Immutable means the existing string cannot be edited.

s = "python"

# s[0] = "P"   # TypeError

Python protects the original string and creates a new one whenever a change is needed.

5. Method call flow

String methods return a new string.

s = "python"

print(s.upper())   # PYTHON
print(s)           # python

To permanently update:

s = s.upper()

6. Method map (visual classification)

Instead of memorizing methods individually, organize them into five families.

Group	Methods
Case	capitalize(), title(), upper(), lower(), swapcase()
Checks	isupper(), islower(), isdigit(), isalpha(), isalnum(), isspace()
Search	index(), count(), startswith(), endswith()
Trim	lstrip(), rstrip(), strip()
Split / Join	split(), join()

7. Universal syntax pattern

Every string method follows the same structure.

text.method()

# Save the returned value
text = text.method()

name = "abraham"

print(name.upper())
print(name.title())

name = name.upper()

Quick knowledge check

Q1. What is the output?

s = "python"
print(s[2])

Answer: t

Q2. What is the result of slicing?

s = "python"
print(s[1:5])

Answer: ytho

Q3. Which statement is correct?

• upper() changes the existing string
• upper() returns a new string ✓

30-second revision sheet

Concept	Syntax
Indexing	s[0]
Slicing	s[1:4]
Method	s.upper()
Reassign	s = s.upper()

Golden rule: Index → Read · Slice → Extract · Methods → Return new · Reassign → Save

Next: Case Conversion Methods.