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Binary File Reading (BMP Example) in Python

In this exercise, you will develop a Python program that verifies if a BMP image file is valid by checking its header. This exercise is perfect for practicing file handling, byte manipulation, and validation in Python. By implementing this program, you will gain hands-on experience in handling file operations, byte manipulation, and validation in Python. This exercise not only reinforces your understanding of file handling but also helps you develop efficient coding practices for managing user interactions.



Group

Managing Files in Python

Objective

Develop a Python program that verifies if a BMP image file is valid by checking its header.

The program should read the file and confirm that the first two bytes match "B" and "M" (ASCII codes 0x42 and 0x4D). If they do, it indicates that the file is potentially a valid BMP image.

Example Python Exercise

 Copy Python Code 
def verify_bmp_header(file_name):
    """
    Verifies if the given file is a valid BMP image by checking its header.
    
    Parameters:
    file_name (str): The name of the file to check.
    
    Returns:
    bool: True if the file is a valid BMP, False otherwise.
    """
    try:
        with open(file_name, 'rb') as file:
            # Read the first two bytes of the file
            header = file.read(2)
            
            # Check if the first two bytes match 'B' and 'M' (0x42 and 0x4D)
            if header == b'BM':
                return True
            else:
                return False
            
    except FileNotFoundError:
        print(f"The file '{file_name}' was not found.")
        return False
    except Exception as e:
        print(f"An error occurred: {e}")
        return False

# Main program execution
if __name__ == "__main__":
    # Ask the user to input the file name
    file_name = input("Please enter the BMP file name to verify: ")
    
    # Verify if the file is a valid BMP image
    if verify_bmp_header(file_name):
        print(f"The file '{file_name}' is a valid BMP image.")
    else:
        print(f"The file '{file_name}' is not a valid BMP image.")

 Output

Assume you have a BMP file named image.bmp. When you run the program, it will behave as follows:

Please enter the BMP file name to verify: image.bmp
The file 'image.bmp' is a valid BMP image.

If the file is not a BMP or the header does not match "BM", the program will output:

Please enter the BMP file name to verify: image.jpg
The file 'image.jpg' is not a valid BMP image.

If the file does not exist, it will output:

Please enter the BMP file name to verify: nonexistent.bmp
The file 'nonexistent.bmp' was not found.

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