Strings in Python

Strings are sequences of characters enclosed in quotes.
They are one of the most common data types in Python.

Why use strings?

Strings are used to store and manipulate text data.
They are essential for user input, messages, and data from files.
Useful for parsing, formatting, and displaying information.
Strings are widely used in web applications, reports, logs, and databases.

Examples of real-time usage:

Usernames or passwords: "Amit123"
Messages in a chat application: "Hello, how are you?"
File paths: "C:/Users/Documents/file.txt"
Displaying formatted reports: "Total sales: $2500"
Storing CSV or JSON data temporarily before processing

We will cover:

Creating strings
String indexing and slicing
String methods
String formatting
Common operations

# ---- Example: creating strings ----
# Strings can be created using single, double, or triple quotes

str1 = "Hello"           # double quotes
str2 = 'Python'          # single quotes
str3 = """This is a 
multiline string"""      # triple quotes for multiple lines

print(str1)
print(str2)
print(str3)

Hello
Python
This is a
multiline string

Example: indexing and slicing

# ---- Example: indexing and slicing ----
# Each character has an index starting from 0
# Slicing allows extracting a part of the string

text = "Python"

print("First character:", text[0])       # P
print("Last character:", text[-1])       # n
print("Slice [0:4]:", text[0:4])         # characters 0 to 3 → 'Pyth'
print("Slice [2:]:", text[2:])           # characters from index 2 to end → 'thon'
print("Slice [:3]:", text[:3])           # first three characters → 'Pyt'

First character: P
Last character: n
Slice [0:4]: Pyth
Slice [2:]: thon
Slice [:3]: Pyt

Example: string methods

# ---- Example: string methods ----
# Useful built-in functions to manipulate strings

s = "python programming"

print("Uppercase:", s.upper())           # converts all letters to uppercase
print("Lowercase:", s.lower())           # converts all letters to lowercase
print("Title case:", s.title())          # capitalizes first letter of each word
print("Count 'p':", s.count('p'))        # counts occurrences of 'p'
print("Find 'program':", s.find('program'))  # returns starting index of substring
print("Replace 'python' with 'Java':", s.replace("python", "Java"))

Uppercase: PYTHON PROGRAMMING
Lowercase: python programming
Title case: Python Programming
Count ‘p’: 2
Find ‘program’: 7
Replace ‘python’ with ‘Java’: Java programming

Example: string formatting

# ---- Example: string formatting ----
# Combine variables and text in readable way

name = "Amit"
age = 25

# Using f-strings (Python 3.6+)
print(f"My name is {name} and I am {age} years old.")

# Using format() method
print("My name is {} and I am {} years old.".format(name, age))

# Using concatenation (less preferred)
print("My name is " + name + " and I am " + str(age) + " years old.")

My name is Amit and I am 25 years old.
My name is Amit and I am 25 years old.
My name is Amit and I am 25 years old.

Example: common string operations

# ---- Example: common string operations ----
s = "Python"

print("Length of string:", len(s))      # number of characters
print("Check if 'Py' in string:", "Py" in s)    # membership test
print("Repeat string:", s * 3)          # repeats string 3 times

Length of string: 6
Check if ‘Py’ in string: True
Repeat string: PythonPythonPython

Summary

We learned about strings in Python:

How to create strings using single, double, or triple quotes
Accessing characters with indexing and slicing
Common string methods: upper(), lower(), title(), count(), find(), replace()
Formatting strings: f-strings, format(), concatenation
Other operations: length, membership test, repetition

Next notebook: 02_lists.ipynb