Python reading file in reverse - efficient way

Efficiently Reading a File in Reverse in Python

def read_file_reverse_efficient(filepath):
    """Reads a file line by line in reverse order efficiently.

    Args:
        filepath: The path to the file.

    Yields:
        Each line of the file in reverse order.
    """

    with open(filepath, 'rb') as f: # Open in binary mode for seeking
        f.seek(0, 2) # Seek to the end of the file
        position = f.tell()

        line = ""
        while position >= 0:
            f.seek(position)
            next_char = f.read(1).decode('utf-8', errors='ignore') # Decode assuming utf-8

            if next_char == '\n':
                if line: # Yield only if the line isn't empty (handles trailing newlines)
                    yield line[::-1] # Reverse the constructed line
                line = "" 
            else:
                line += next_char

            position -= 1 # move back to the previous character

        if line: # Yield the first line (last in reverse) if it exists
            yield line[::-1] 

# Example usage:
filepath = "your_file.txt" # Replace with your file path
for line in read_file_reverse_efficient(filepath):
    print(line)

Explanation and Efficiency Improvements:

1. Binary Mode and Seeking: Opens the file in binary mode ('rb') which is essential for accurate seeking. We use f.seek(0, 2) to move the file pointer directly to the end of the file. This avoids reading the entire file into memory at once.
2. Character-by-Character Reading: The code reads the file character by character backwards using f.read(1). This minimizes memory usage as we only hold one character in memory at a time (plus the current line being built).
3. UTF-8 Decoding with Error Handling: Decodes the byte read from the file assuming UTF-8 encoding. The errors='ignore' handles potential decoding errors gracefully.
4. Reverse Line Construction: The line string is built in reverse order. We then efficiently reverse it once with line[::-1] before yielding, which is faster than repeatedly prepending characters.
5. Handling Trailing Newlines: The code correctly handles potential trailing newlines.

Key Differences from Less Efficient Approaches:

• No readlines(): Avoids reading the entire file into a list, which is memory-intensive for large files.
• Optimized Reverse: The [::-1] slicing for reversing is efficient.
• Binary Mode Seeking: More precise and reliable.

This improved version is memory-efficient, suitable even for very large files.