Python String

In Python, a string is a sequence of characters enclosed in either single quotes (') or double quotes ("). Here’s an example:

my_string = "Hello, world!"

n addition to regular characters, a string can also contain special characters such as newlines (\n), tabs (\t), and backslashes (\\). For example:

my_string = "Hello, world!\nThis is a new line.\tThis is a tab.\\" 

Strings in Python are immutable, which means that once you create a string, you can’t change its contents. However, you can create a new string by manipulating the original one using various methods and operations. Here are some common string operations in Python:

• Concatenation: You can concatenate two strings using the + operator. For example:

• first_name = "John"
  last_name = "Doe"
  full_name = first_name + " " + last_name  # full_name = "John Doe"
  

  String interpolation: You can insert variables and expressions into a string using the format() method or f-strings (available from Python 3.6 onwards). For example:

  name = "John"
  age = 30
  message = "My name is {} and I'm {} years old.".format(name, age)
  message = f"My name is {name} and I'm {age} years old."
  

  String slicing: You can extract a portion of a string using the slice notation [start:stop:step]. For example:

my_string = "Hello, world!"
print(my_string[0:5])  # Output: "Hello"
print(my_string[7:])   # Output: "world!"
print(my_string[::-1]) # Output: "!dlrow ,olleH"

There are many other operations and methods you can perform on strings in Python, such as finding substrings, replacing parts of a string, converting to uppercase or lowercase, and more.

String Operators:

In Python, there are several operators that can be used with strings:

1. Concatenation Operator (+): The concatenation operator + is used to join two strings together. For example:

str1 = "Hello"
str2 = "World"
result = str1 + " " + str2
print(result) # Output: "Hello World"

2. Repetition Operator (*): The repetition operator * is used to repeat a string a given number of times. For example:

str1 = "Hello"
result = str1 * 3
print(result) # Output: "HelloHelloHello"

3. Membership Operator (in): The membership operator in is used to check if a string is a substring of another string. For example:

str1 = "Hello World"
if "World" in str1:
    print("Substring Found")
else:
    print("Substring Not Found")

4. Index Operator ([]): The index operator [] is used to access a specific character or substring of a string. For example:

str1 = "Hello World"
print(str1[0])   # Output: "H"
print(str1[6:11]) # Output: "World"

5. Slice Operator ([:]): The slice operator [:] is used to extract a portion of a string. For example:

str1 = "Hello World"
print(str1[:5])  # Output: "Hello"
print(str1[6:])  # Output: "World"

6. Comparison Operators (==, !=, <, >, <=, >=): Comparison operators can be used to compare two strings. Strings are compared based on their lexicographic order (i.e., alphabetical order). For example:

str1 = "apple"
str2 = "banana"
if str1 < str2:
    print("str1 comes before str2")
else:
    print("str2 comes before str1")

These are some of the commonly used string operators in Python.

Python String Formatting:

Python provides several ways to format strings, including:

1. String Interpolation using f-strings: f-strings (also known as formatted string literals) were introduced in Python 3.6. They allow you to embed expressions inside string literals, using curly braces {}. The expressions inside the braces are evaluated at runtime and their values are inserted into the string. For example:

name = "John"
age = 30
message = f"My name is {name} and I'm {age} years old."
print(message) # Output: "My name is John and I'm 30 years old."

2. Using the str.format() method: The str.format() method allows you to insert values into a string by specifying placeholders inside the string and passing the values as arguments to the format() method. Placeholders are represented by curly braces {}. For example:

name = "John"
age = 30
message = "My name is {} and I'm {} years old.".format(name, age)
print(message) # Output: "My name is John and I'm 30 years old."

You can also use numbered placeholders {0}, {1}, etc., to specify the order of the arguments passed to the format() method.

3. Using % operator: The % operator can also be used for string formatting. It works by using placeholders (similar to the str.format() method) and passing values as a tuple. For example:

name = "John"
age = 30
message = "My name is %s and I'm %d years old." % (name, age)
print(message) # Output: "My name is John and I'm 30 years old."

In the above example, %s is a placeholder for a string and %d is a placeholder for an integer.

String formatting allows you to create dynamic and formatted strings based on the values of variables and expressions. It is a powerful feature in Python and is widely used in many applications.

The format() method:

The format() method is a built-in method in Python that allows you to format strings dynamically. It can be used to insert values into a string and specify how they should be formatted, such as specifying the number of decimal places for a floating-point number, the width of a field, and so on.

The format() method works by replacing placeholders inside a string with values passed as arguments to the method. Placeholders are represented by curly braces {}. You can specify the position of the argument to be inserted using an index inside the braces. For example:

name = "John"
age = 30
message = "My name is {} and I'm {} years old.".format(name, age)
print(message) # Output: "My name is John and I'm 30 years old."

pi = 3.141592653589793
formatted_pi = "{:.2f}".format(pi)
print(formatted_pi) # Output: "3.14"

age = 30
message = "I'm %d years old." % age
print(message) # Output: "I'm 30 years old."

pi = 3.141592653589793
formatted_pi = "Pi is approximately equal to %.2f." % pi
print(formatted_pi) # Output: "Pi is approximately equal to 3.14."

name = "John"
message = "Hello, %s!" % name
print(message) # Output: "Hello, John!"

name = "John"
age = 30
message = "My name is %s and I'm %d years old." % (name, age)
print(message) # Output: "My name is John and I'm 30 years old."

my_string = "Hello, world!"
length = len(my_string)
print(length) # Output: 13

my_string = "Hello, World!"
lowercase_string = my_string.lower()
print(lowercase_string) # Output: "hello, world!"

my_string = "Hello, World!"
uppercase_string = my_string.upper()
print(uppercase_string) # Output: "HELLO, WORLD!"

my_string = "  Hello, world!  "
stripped_string = my_string.strip()
print(stripped_string) # Output: "Hello, world!"

my_string = "Hello, World!"
new_string = my_string.replace("World", "Python")
print(new_string) # Output: "Hello, Python!"

my_string = "Hello, World!"
my_list = my_string.split(",")
print(my_list) # Output: ["Hello", " World!"]

my_list = ["Hello", "World"]
my_string = ", ".join(my_list)
print(my_string) # Output: "Hello, World"