Strings

On This Page

• 3.1  String Creation
• 3.2  Indexing
• 3.3  Slicing
• 3.4  Escape Characters
• 3.5  String Formatting
• 3.6  Important String Methods
• 3.7  Practical Exercises
• 3.8  Module Quiz (MCQs)
• 3.9  Module Assignment
• 3.10  Interview Questions — Module 3
• 3.11  Student Notes Page

Module 3: Strings

3.1  String Creation

A string is a sequence of characters enclosed in quotes. Python allows single, double, and triple quotes — all work the same way, giving you flexibility when text itself contains quotes.

s1 = 'Samantus'
s2 = "Web Training Institute"
s3 = """This is a
multi-line string"""

print(s1, s2)
print(s3)

3.2  Indexing

Every character in a string has a position number called an index. Python indexing starts at 0, and negative indexes count from the end of the string.

course = "PYTHON"
print(course[0])   # first character
print(course[5])   # last character
print(course[-1])  # last character (negative index)
print(course[-6])  # first character (negative index)

3.3  Slicing

Slicing lets you extract a portion (substring) of a string using the format string[start:stop:step]. The stop index is never included.

text = "Samantus Web Training"
print(text[0:8])     # Samantus
print(text[9:12])    # Web
print(text[:8])      # from start to index 8
print(text[9:])      # from index 9 to end
print(text[::-1])    # reversed string

3.4  Escape Characters

Escape characters let you include special characters (like quotes or new lines) inside a string using a backslash \.

print("Samantus\nWeb Training Institute")
print("Course:\tPython for Data Analytics")
print('It\'s a great course')

3.5  String Formatting

String formatting lets you insert variable values neatly into text. The modern, recommended way is using f-strings (formatted string literals).

name = "Priya"
fee = 15000

# 1. f-string (recommended)
print(f"{name} paid Rs.{fee}")

# 2. .format() method
print("{} paid Rs.{}".format(name, fee))

# 3. % operator (older style)
print("%s paid Rs.%d" % (name, fee))

3.6  Important String Methods

Python strings come with many built-in methods for cleaning, searching, and transforming text.

email = "  STUDENT@GMAIL.COM  "
clean_email = email.strip().lower()
print(clean_email)

course = "Digital Marketing, SEO, Google Ads"
skills = course.split(", ")
print(skills)

3.7  Practical Exercises

Basic (5 Questions)

1. Store your full name in a string and print its length using len().

2. Print the first and last character of your name using indexing.

3. Convert your name to all uppercase and all lowercase.

4. Use slicing to print only the first 3 letters of 'Samantus'.

5. Use an escape character to print your name and course on two separate lines.

Intermediate (5 Questions)

1. Take a sentence as input and print it in reverse using slicing.

2. Clean a messy string with extra spaces and mixed case using strip() and lower().

3. Split a comma-separated string of skills into a list and print each skill on its own line.

4. Use replace() to change all occurrences of one word in a sentence to another word.

5. Write an f-string that combines a student's name, course, and fee into one formatted sentence.

Advanced (5 Questions)

1. Write a program to check if a given string is a palindrome (reads the same forwards and backwards).

2. Count how many times a specific letter appears in a paragraph of text.

3. Take a full email address and extract just the username part (before the @) using slicing or split().

4. Write a program that takes a sentence and capitalizes the first letter of every word.

5. Build a simple 'Data Cleaner': take a messy string with extra spaces/mixed case and return a clean, title-cased version.

3.8  Module Quiz (MCQs)

3.9  Module Assignment

Assignment: Student Data Cleaner

• Take a messy student name as input (e.g. ' priya SHARMA ').
• Clean it using strip() and format it in proper Title Case.
• Take a comma-separated list of the student's enrolled courses and split it into a list.
• Print a final formatted summary using an f-string: 'Student: ___ | Courses: ___'.

Expected Output: A clean, properly-cased student name and a Python list of their courses, displayed together in one neatly formatted output line.

3.10  Interview Questions — Module 3

• Q: What is the difference between indexing and slicing?
  A: Indexing retrieves a single character at a specific position, while slicing extracts a range (substring) of characters using a start and stop position.
• Q: Are strings mutable or immutable in Python?
  A: Strings are immutable — once created, their characters cannot be changed in place; any 'modification' actually creates a new string.
• Q: What is the difference between split() and join()?
  A: split() breaks a string into a list based on a separator, while join() combines a list of strings into one string using a specified separator.
• Q: How would you check if a string starts with a specific prefix?
  A: Use the startswith() method, e.g. "report.csv".startswith("report") returns True.

3.11  Student Notes Page

Use this space to write down key points, doubts, and your own examples from today's session.