Python - Reading and Writing Files

The seek() method in Python is used to change the current position of the file pointer within a file. It allows you to move the file pointer to a specific byte offset or position in the file. This is useful when you want to navigate to a particular location in the file before performing read or write operations.

Here's an example program that demonstrates the purpose of the seek() method:

# Open the file in read mode
with open('example.txt', 'r') as file:
    # Read the first 10 characters from the file
    content_part1 = file.read(10)
    print("Content Part 1:", content_part1)

    # Use seek() to move the file pointer to position 15
    file.seek(15)

    # Read the next 5 characters from the new position
    content_part2 = file.read(5)
    print("Content Part 2:", content_part2)

In this example, the file 'example.txt' is opened in read mode using the with statement. The read() method is used to read the first 10 characters of the file. The seek() method is then used to move the file pointer to position 15, and another read() operation is performed to read the next 5 characters from the new position.

The output of the program will be:

Content Part 1: This is th
Content Part 2: e firs

The tell() method in Python is used to determine the current position of the file pointer within a file. It returns the byte offset from the beginning of the file where the next read or write operation will occur. The tell() method is helpful for keeping track of the file pointer's position during file handling operations.

Here's an example program that demonstrates the role of the tell() method:

# Open the file in read mode
with open('example.txt', 'r') as file:
    # Read the first 15 characters from the file
    content_part1 = file.read(15)
    print("Content Part 1:", content_part1)

    # Use tell() to get the current position of the file pointer
    current_position = file.tell()
    print("Current File Pointer Position:", current_position)

    # Read the next 10 characters from the current position
    content_part2 = file.read(10)
    print("Content Part 2:", content_part2)

In this example, the file 'example.txt' is opened in read mode using the with statement. The read() method is used to read the first 15 characters of the file. The tell() method is then used to get the current position of the file pointer, and another read() operation is performed to read the next 10 characters from the current position.

The output of the program will be:

Content Part 1: This is the con
Current File Pointer Position: 15
Content Part 2: tent of the

In Python, you can check if a file exists before opening it using the os.path.exists() function from the os module. This function returns True if the specified path exists, and False otherwise.

import os

# Specify the file path
file_path = 'example.txt'

# Check if the file exists
if os.path.exists(file_path):
    # Open the file if it exists
    with open(file_path, 'r') as file:
        content = file.read()
        print("File Content:")
        print(content)
else:
    print(f"The file '{file_path}' does not exist.")

In this example, the file path is specified, and the os.path.exists() function is used to check if the file exists. If the file exists, it is opened in read mode using the with statement, and its content is read and printed. If the file does not exist, a message is printed indicating that the file does not exist.

The output of the program will depend on whether the file 'example.txt' exists in the specified path.

In Python, a context manager is an object that defines the methods __enter__() and __exit__(). Context managers are used to set up and tear down resources, and they are commonly employed with the with statement. The with statement ensures that the context manager's __enter__() method is called before the block of code inside the with statement is executed, and the __exit__() method is called afterward, even if an exception is raised.

Context managers are especially useful in file handling to ensure that files are properly opened and closed, even in the presence of exceptions or errors.

class CustomFileContextManager:
    def __init__(self, file_path, mode):
        self.file_path = file_path
        self.mode = mode
        self.file = None

    def __enter__(self):
        # Open the file and return the file object
        self.file = open(self.file_path, self.mode)
        return self.file

    def __exit__(self, exc_type, exc_value, traceback):
        # Close the file in the __exit__ method
        if self.file:
            self.file.close()

# Usage of the custom context manager
file_path = 'example.txt'
mode = 'r'

# Using the context manager with the with statement
with CustomFileContextManager(file_path, mode) as file:
    # Perform file operations within the with block
    content = file.read()
    print("File Content:")
    print(content)

In this example, the CustomFileContextManager class is created to manage file resources. The __enter__() method opens the file and returns the file object, which is then accessible within the with block. The __exit__() method ensures that the file is closed, even if an exception occurs.

The output of the program will depend on the content of the file 'example.txt'.