Python String Tutorial

Introduction

Strings in Python are sequences of characters enclosed in quotes. They can be enclosed in single quotes ('), double quotes ("), or triple quotes (''' or """). Strings are immutable, meaning their contents cannot be changed once created. This tutorial covers various operations and features of strings in Python.

Table of Contents

1. Define String and Key Points
2. Create String
3. Access String Characters
4. Change String Characters
5. Concatenate Strings
6. String Methods
7. String Formatting
8. String Slicing
9. Loop Through a String
10. String Operations
11. String Methods
12. Conclusion

Key Points

Strings in Python are sequences of characters enclosed in quotes. They can be enclosed in single quotes ('), double quotes ("), or triple quotes (''' or """). 

Key points about strings:

• Immutable: Contents cannot be changed after creation.
• Indexed: Each character is accessible using its index.
• Sequence: Strings are sequences of characters.

1. Create String

Strings can be created by enclosing characters in single, double, or triple quotes.

Example

# Creating strings
single_quote_str = 'Hello'
double_quote_str = "Hello"
triple_quote_str = '''Hello, this is a multi-line string.'''

print(single_quote_str)  # Output: Hello
print(double_quote_str)  # Output: Hello
print(triple_quote_str)  # Output: Hello, this is a multi-line string.

2. Access String Characters

String characters can be accessed using their index. Indexing starts at 0. Negative indexing is also supported.

Example

my_string = "Python"

# Accessing characters
print(my_string[0])  # Output: P
print(my_string[3])  # Output: h

# Negative indexing
print(my_string[-1])  # Output: n
print(my_string[-2])  # Output: o

3. Change String Characters

Since strings are immutable, you cannot change their characters directly. However, you can create a new string with the desired modifications.

Example

# Attempting to change a character (will raise an error)
# my_string[0] = 'J'  # TypeError: 'str' object does not support item assignment

# Creating a new string with the desired changes
new_string = 'J' + my_string[1:]
print(new_string)  # Output: Jython

4. Concatenate Strings

Strings can be concatenated using the + operator or join() method.

Example

str1 = "Hello"
str2 = "World"

# Using + operator
concatenated_str = str1 + " " + str2
print(concatenated_str)  # Output: Hello World

# Using join() method
concatenated_str = " ".join([str1, str2])
print(concatenated_str)  # Output: Hello World

5. String Methods

Python provides various built-in methods for string manipulation.

Example

sample_str = " Hello, World! "

# strip() method
print(sample_str.strip())  # Output: Hello, World!

# lower() method
print(sample_str.lower())  # Output:  hello, world!

# upper() method
print(sample_str.upper())  # Output:  HELLO, WORLD!

# replace() method
print(sample_str.replace("World", "Python"))  # Output:  Hello, Python!

# split() method
print(sample_str.split(","))  # Output: [' Hello', ' World! ']

6. String Formatting

Python supports several ways to format strings, including f-strings, format(), and % operator.

Example

name = "Ravi"
age = 25

# Using f-strings
formatted_str = f"My name is {name} and I am {age} years old."
print(formatted_str)  # Output: My name is Ravi and I am 25 years old.

# Using format() method
formatted_str = "My name is {} and I am {} years old.".format(name, age)
print(formatted_str)  # Output: My name is Ravi and I am 25 years old.

# Using % operator
formatted_str = "My name is %s and I am %d years old." % (name, age)
print(formatted_str)  # Output: My name is Ravi and I am 25 years old.

7. String Slicing

String slicing allows you to extract a part of a string by specifying a range of indices.

Example

my_string = "Hello, World!"

# Slicing a string
sliced_str = my_string[0:5]
print(sliced_str)  # Output: Hello

# Slicing with negative indices
sliced_str = my_string[-6:-1]
print(sliced_str)  # Output: World

# Slicing with step
sliced_str = my_string[0:12:2]
print(sliced_str)  # Output: Hlo ol

8. Loop Through a String

You can loop through the characters in a string using a for loop.

Example

for char in "Python":
    print(char)

# Output:
# P
# y
# t
# h
# o
# n

9. String Operations

Python strings support various operations, including checking for substrings, repeating, and more.

Example

my_string = "Python"

# Checking for substring
print("Pyt" in my_string)  # Output: True
print("Java" in my_string)  # Output: False

# Repeating a string
repeated_str = my_string * 3
print(repeated_str)  # Output: PythonPythonPython

10. String Methods

Python strings come with many built-in methods for various tasks. Here are some commonly used ones:

Example

example_str = "python programming"

# capitalize() method
print(example_str.capitalize())  # Output: Python programming

# count() method
print(example_str.count("p"))  # Output: 2

# find() method
print(example_str.find("gram"))  # Output: 10

# isalpha() method
print(example_str.isalpha())  # Output: False (because of the space)

# isdigit() method
print("12345".isdigit())  # Output: True

# join() method
print(", ".join(["apple", "banana", "cherry"]))  # Output: apple, banana, cherry

# startswith() method
print(example_str.startswith("py"))  # Output: True

# endswith() method
print(example_str.endswith("ing"))  # Output: True

Conclusion

Strings are fundamental in Python and are used to store and manipulate text. Understanding how to create, access, modify, and perform operations on strings is essential for effective programming. This tutorial covered various aspects of strings, including creating, accessing, changing, and removing items, as well as advanced topics like string slicing, formatting, looping, and using built-in methods. By mastering these concepts, you can efficiently work with strings in your Python programs.