Working with Strings

Table Of Content:

Basics of Python Strings:

In Python, strings are sequences of characters enclosed in single quotes (') or double quotes ("). Here’s how you create strings:

# Single quotes
single_quoted = 'Hello, World!'

# Double quotes
double_quoted = "Hello, World!"

Accessing Characters:

Strings are indexed starting from 0. You can access characters using square brackets []:

my_string = "Python"
print(my_string[0])  
print(my_string[1])  

Output:

'P'
'y'

String Length:

You can find the length of a string using the len() function:

my_string = "Python"
print(len(my_string))  

Output:

  6

Concatenating Strings:

Strings can be concatenated using the + operator:

string1 = "Hello"
string2 = "World"
concatenated_string = string1 + " " + string2
print(concatenated_string) 

Output:

'Hello World'

String Methods:

Python strings have many built-in methods for manipulation:

my_string = "  Hello, World!  "
print(my_string.strip())  # Remove leading and trailing whitespace

print(my_string.lower())  # Convert to lowercase

print(my_string.upper())  # Convert to uppercase

print(my_string.replace("Hello", "Hi")) # Replace substring

print(my_string.split(","))  # Split string into a list

Output:

 'Hello, World!'
 '  hello, world!  ' 
'  HELLO, WORLD!  '
'  Hi, World!  '
 ['  Hello', ' World!  ']

Advanced Concepts:

String Formatting:

Python offers several ways to format strings. Here’s an example using f-strings (formatted string literals):

name = "Alice"
age = 30
formatted_string = f"My name is {name} and I am {age} years old."
print(formatted_string)

Output:

'My name is Alice and I am 30 years old.'

Unicode Strings:

Python natively supports Unicode, allowing you to handle international characters:

unicode_string = "こんにちは"
print(unicode_string)

Raw Strings:

Raw strings treat backslashes (\) as literal characters, useful for regular expressions and file paths:

raw_string = r'C:\path\to\file.txt'
print(raw_string)  
  

Output:

C:\path\to\file.txt'

String Slicing:

You can slice strings to extract substrings.

my_string = "Python Programming"
print(my_string[0:6])  # Slice from index 0 to 5

print(my_string[-11:-1]) 

Output:

'Python'
'Programming'

Example:

# Example: Counting vowels in a string
def count_vowels(string):
    vowels = "aeiouAEIOU"
    count = 0
    for char in string:
        if char in vowels:
            count += 1
    return count

input_string = "Hello, how are you?"
print(f"The number of vowels in '{input_string}' is: {count_vowels(input_string)}")

Output:

The number of vowels in 'Hello, how are you?' is: 6

In this example:

• We define a function count_vowels() that counts vowels in a given string.
• We use an input string "Hello, how are you?".
• Output shows the count of vowels in the input string.

This covers a range of string operations from basic manipulation to more advanced concepts like Unicode handling and string formatting.

Interview Questions:

Question 1: How do you create a string in Python?

Answer: Strings in Python are created by enclosing characters in single (') or double (") quotes.

 Question 2: How can you access characters in a string?

 Answer: Characters in a string can be accessed using indexing. For example, my_string[0] accesses the first character.

 Question 3: How do you find the length of a string in Python?

Answer: Strings can be concatenated using the + operator.