Handling Strings in Python

A string is a collection of characters enclosed in single quotes ('), double quotes ("), or triple quotes (''' or """). While triple quotes are often used for multiline strings, Python treats single characters as strings with a length of 1 since it does not have a separate character data type.

Accessing Characters in a String

Strings are collections of characters, and each character can be accessed using its index. Python indexing starts from:

• 0 for the first character (forward indexing).
• -1 for the last character (backward indexing).

Visual Representation of Indexing

To better understand indexing, refer to the image below:

Example:

String1 = "PYTHONFORALL"
 
# Accessing characters using forward indexing
print(String1[3])   # Output: H
 
# Accessing characters using backward indexing
print(String1[-3])  # Output: A

Important Note:

Providing an index out of range will result in an IndexError.

Escape Sequences in Strings

Escape sequences allow you to include special characters in strings that cannot be directly typed. They begin with a backslash (\).

Example:

# Using escape sequences
print("Python says \"Learn Strings!\"")
print("Path: C:\\Users\\YourName")
print("Hello\nWorld")

String Operations

1. Concatenation

Concatenation is the process of joining two strings using the + operator.

Example:

name = "Rhea"
msg = "Hello "
print(msg + name)  # Output: Hello Rhea

2. Repetition/Replication

Replication repeats the string n times using the * operator.

Example:

name = "PythonForAll"
print(name * 4)  # Output: PythonForAllPythonForAllPythonForAllPythonForAll

3. Slicing

Slicing extracts a substring from the main string based on specified index values.

Example:

name = "PythonForAll"
 
# Slice using forward indexing
print(name[0:6])  # Output: Python
 
# Slice using backward indexing
print(name[-6:-2])  # Output: ForA
 
# Slice with step value
print(name[1:8:2])  # Output: yhno
 
# Reverse the string
print(name[::-1])  # Output: llAroFnohtyP

Membership Operators in Strings

Python uses in and not in operators to check for the presence of substrings in a string.

Example:

name = "PythonForAll"
 
# Using 'in'
print("on" in name)  # Output: True
 
# Using 'not in'
print("All" not in name)  # Output: True

Built-In String Functions

Python provides several built-in functions to manipulate strings. Here are some commonly used ones:

Examples

Example 1: Menu-Based String Manipulation

# Menu-Based String Manipulation
option = int(input("Choose an option (1: Uppercase, 2: Lowercase): "))
text = input("Enter a string: ")
 
if option == 1:
    print("Uppercase:", text.upper())
elif option == 2:
    print("Lowercase:", text.lower())
else:
    print("Invalid option")

Example 2: Toggle Case

# Toggle Case
text = input("Enter a string: ")
print("Toggled Case:", text.swapcase())

Example 3: Check Palindrome

# Check Palindrome (Without Slicing)
text = input("Enter a string: ")
reversed_text = ''.join(reversed(text))
 
if text == reversed_text:
    print(text, "is a palindrome")
else:
    print(text, "is not a palindrome")

Try It Yourself

Problem 1: Count Vowels

Write a program to input a string and count the number of vowels (a, e, i, o, u) in it.

text = input("Enter a string: ")
vowels = "aeiouAEIOU"
count = 0
 
for char in text:
    if char in vowels:
        count += 1
 
print("Number of vowels:", count)

Problem 2: Replace Substring

Write a program to input a string and replace all spaces with underscores (_).

text = input("Enter a string: ")
print("Modified string:", text.replace(" ", "_"))

Problem 3: Reverse a String

Write a program to input a string and print it in reverse order.

text = input("Enter a string: ")
print("Reversed string:", text[::-1])