Python Strings

A string in Python is a sequence of characters enclosed in single, double, or triple quotes. Strings are one of the most widely used data types in Python, representing text data.

What is a String?

A string is a collection of characters enclosed within quotes. Python provides several ways to define and manipulate strings. Strings are immutable, meaning that once created, they cannot be altered.

Creating a String

Strings in Python can be created by enclosing characters in either single quotes (') or double quotes (").

# Creating strings in Python
str1 = 'Hello, World!'  # Single quotes
str2 = "Python is awesome"  # Double quotes
str3 = '''This is a 
multi-line string'''  # Triple quotes for multi-line strings
            

Explanation:

Here, str1, str2, and str3 are examples of strings created with single quotes, double quotes, and triple quotes, respectively. Triple quotes are especially useful for multi-line strings.

String Indexing and Slicing

Strings in Python are indexed, meaning each character in a string has a corresponding index number. The index starts from 0 for the first character. Negative indexing can also be used to access characters from the end of the string.

Indexing Syntax

# Indexing and Slicing a string
str = "Python"
first_char = str[0]  # Access first character (P)
last_char = str[-1]  # Access last character (n)
substring = str[1:4]  # Access substring (yt)
            

Explanation:

• str[0] accesses the first character P.
• str[-1] accesses the last character n.
• str[1:4] slices the string from index 1 to 3, returning yt.

String Concatenation

String concatenation in Python can be done using the + operator. This operator joins two or more strings together.

# Concatenating strings in Python
str1 = "Hello"
str2 = "World"
result = str1 + " " + str2  # Concatenates two strings with a space
            

Explanation:

Here, str1 + " " + str2 concatenates the two strings str1 and str2, adding a space between them. The result will be the string "Hello World".

String Methods

Python provides several built-in methods to perform common operations on strings. These methods allow us to manipulate strings efficiently. Below are some common string methods:

str = "Python Programming"
upper_case = str.upper()  # Converts to uppercase
lower_case = str.lower()  # Converts to lowercase
count_python = str.count("Python")  # Counts occurrences of 'Python'
replace_programming = str.replace("Programming", "Coding")  # Replace 'Programming' with 'Coding'
split_words = str.split()  # Splits the string into a list of words
            

Explanation:

In the above example:

• str.upper() converts the string to uppercase.
• str.lower() converts the string to lowercase.
• str.count("Python") counts how many times the word "Python" appears in the string.
• str.replace("Programming", "Coding") replaces "Programming" with "Coding".
• str.split() splits the string into a list of words, using spaces as delimiters.

String Escape Characters

Python allows you to use special characters in strings called escape characters. These characters are preceded by a backslash () and serve various purposes, such as inserting new lines, tabs, or quotes inside strings.

Common Escape Characters:

• n: Newline
• t: Tab
• ': Single quote
• ": Double quote
• : Backslash

# Escape characters in Python strings
str1 = "HellonWorld"  # New line between Hello and World
str2 = "PythontProgramming"  # Tab between Python and Programming
str3 = "He said, "Python is awesome!""  # Double quotes inside string
str4 = "This is a backslash: "  # Display a backslash
            

Explanation:

• n creates a new line between "Hello" and "World".
• t adds a tab between "Python" and "Programming".
• " allows double quotes to appear inside the string.
• displays a backslash.

String Formatting

String formatting allows you to embed variables into a string. Python provides several ways to format strings, such as using the % operator, str.format() method, and f-strings (formatted string literals).

# Using % operator for string formatting
name = "Alice"
age = 25
message = "Hello, %s! You are %d years old." % (name, age)
            

Explanation:

# Using str.format() for string formatting
message = "Hello, {}! You are {} years old.".format(name, age)
            

Explanation:

# Using f-strings for string formatting
message = f"Hello, {name}! You are {age} years old."
            

Explanation:

f-strings (formatted string literals) are a concise way to embed expressions inside string literals. They are prefixed with the letter f and expressions are enclosed in curly braces {}.