Python basics - Day 09

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Day 9 – Strings

Project: Build a “String Analyzer” to explore and manipulate text data

01. Learning Goal

By the end of this lesson, you will be able to:

Create and manipulate strings in Python
Access and slice string elements
Use string methods to clean and modify text
Analyze and extract information from text

02. Problem Scenario

Text data is everywhere — from names and emails to user input.

You need to process, clean, and analyze text efficiently.

Your goal today: learn how to slice, join, search, and modify strings.

03. Step 1 – What is a String?

A string is a sequence of characters enclosed in either single ' ' or double " " quotes.

text1 = "Hello"
text2 = 'Python'
print(text1, text2)

04. Step 2 – Indexing and Slicing

Like lists, strings are ordered sequences and support indexing.

word = "Python"

print(word[0])    # P (first character)
print(word[-1])   # n (last character)
print(word[0:4])  # Pyth (from index 0 to 3)
print(word[:2])   # Py
print(word[2:])   # thon

05. Step 3 – String Operations

You can combine (+) or repeat (*) strings easily.

a = "Hello"
b = "World"

print(a + " " + b)   # Concatenation → Hello World
print(a * 3)         # Repetition → HelloHelloHello

06. Step 4 – Common String Methods

Python provides many built-in methods to process strings.

s = "  python programming  "

print(s.upper())      # Convert to uppercase
print(s.lower())      # Convert to lowercase
print(s.strip())      # Remove whitespace
print(s.replace("python", "java"))  # Replace text
print(s.split())      # Split by spaces → ['python', 'programming']

07. Step 5 – String Checks

You can check for substrings and specific patterns.

msg = "Hello Python"

print("Python" in msg)    # True
print("Java" not in msg)  # True

print(msg.startswith("Hello"))  # True
print(msg.endswith("Python"))   # True

08. Step 6 – Using f-Strings

The f-string allows easy variable insertion into text.

name = "Sabin"
lang = "Python"
print(f"{name} is learning {lang}.")

09. Step 7 – Strings and Loops

You can loop through each character in a string.

for ch in "Hello":
    print(ch)

10. Step 8 – Practice Examples

Example 1: Find String Length

s = "Python"
print(len(s))   # 6

Example 2: Extract Username from Email

email = "sabin@test.com"
user = email.split("@")[0]
print("Username:", user)   # sabin

Example 3: Reverse a String

text = "Python"
print(text[::-1])   # nohtyP

11. Step 9 – Mini Project: String Analyzer

Create a simple program that takes a sentence and prints key details.

sentence = input("Enter a sentence: ")

print("Length:", len(sentence))
print("Uppercase:", sentence.upper())
print("Lowercase:", sentence.lower())
print("Reversed:", sentence[::-1])
print("Words:", len(sentence.split()))