0 Splitting a PDF into Left and Right Halves Using Python.md

Splitting a PDF into Left and Right Halves Using Python

Managing and manipulating PDF files is a common task in document processing. Sometimes, you may need to divide each page of a PDF into two halves—such as separating the left and right sides of scanned book pages. The following Python script provides a simple and efficient way to accomplish this using the pypdf library.

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Overview

The script, named split_pdf_halves.py, reads a PDF file and outputs a new one where each page is split into two separate pages: the left half and the right half. It handles both portrait and landscape orientations, as well as page rotation information, ensuring that the resulting pages maintain correct alignment.

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Key Features

• Automatic Page Splitting: Each page is divided exactly in half by its width.
• Rotation Handling: The script respects any rotation metadata, ensuring that the output looks correct.
• Metadata Preservation: Basic document metadata is copied to the new file.
• Customizable Output: You can modify the order or add features like bookmark copying if needed.

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How It Works

1. Reading and Writing PDFs: The script uses PdfReader to open the input file and PdfWriter to create the new output file.

2. Splitting Pages: The split_page_into_left_right() function calculates the midpoint of the page and creates two rectangular regions using RectangleObject. It then crops the original page to create two new pages — one for the left half and one for the right.

3. Rotation Support: Pages with 90°, 180°, or 270° rotation are processed appropriately to ensure the left and right halves are extracted visually correctly.

4. Output Creation: The script adds both new pages (left and right) into the output file sequentially and saves it.

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Usage

To run the script, use the following command in your terminal:

python split_pdf_halves.py input.pdf output.pdf

• input.pdf – the path to your source PDF file.
• output.pdf – the desired name for the new split PDF.

If the input file is missing or the arguments are incorrect, the script will display usage instructions.

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Dependencies

Before running, install the required library:

pip install pypdf

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Conclusion

This Python script offers a quick, reliable way to split PDF pages into left and right halves. It’s especially useful for digitizing double-page scans or reorganizing content for better readability. With a few small modifications, you can extend it to handle bookmarks, annotations, or even custom split ratios, making it a flexible tool for PDF processing workflows.

main.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
A script that splits each page of a PDF into "left half" and "right half" and outputs the result.
Dependencies: pypdf (pip install pypdf)

Usage:
  python split_pdf_halves.py input.pdf output.pdf

Notes:
- The page is split evenly in half by width, regardless of its orientation (portrait/landscape).
- Page rotation information (rotation) is respected to ensure correct splitting.
- Bookmarks, annotations, etc. are not copied (add that functionality if needed).
"""

import sys
from pathlib import Path
from pypdf import PdfReader, PdfWriter, PageObject
from pypdf.generic import RectangleObject

def clone_page(page):
    new_page = PageObject()     # Create an empty PageObject
    new_page.update(page)       # Copy contents (as PageObject)
    return new_page

def split_page_into_left_right(page):
    media = page.mediabox
    x0, y0 = float(media.left), float(media.bottom)
    x1, y1 = float(media.right), float(media.top)
    mid_x = (x0 + x1) / 2.0
    rotation = (page.get("/Rotate") or 0) % 360

    if rotation in (0, 180):
        left_rect  = RectangleObject([x0, y0, mid_x, y1])
        right_rect = RectangleObject([mid_x, y0, x1, y1])
    elif rotation == 90:
        mid_y = (y0 + y1) / 2.0
        left_rect  = RectangleObject([x0, mid_y, x1, y1])  # Visually, left = top
        right_rect = RectangleObject([x0, y0,  x1, mid_y]) # Visually, right = bottom
    elif rotation == 270:
        mid_y = (y0 + y1) / 2.0
        left_rect  = RectangleObject([x0, y0,  x1, mid_y]) # Visually, left = bottom
        right_rect = RectangleObject([x0, mid_y, x1, y1])  # Visually, right = top
    else:
        left_rect  = RectangleObject([x0, y0, mid_x, y1])
        right_rect = RectangleObject([mid_x, y0, x1, y1])

    left_page  = clone_page(page)
    right_page = clone_page(page)

    left_page.cropbox  = left_rect
    right_page.cropbox = right_rect
    left_page.mediabox  = left_rect
    right_page.mediabox = right_rect

    if rotation:
        # In pypdf, using rotate_clockwise is more explicit
        left_page.rotate_clockwise(rotation)
        right_page.rotate_clockwise(rotation)

    return left_page, right_page


def split_pdf(input_path: str, output_path: str):
    reader = PdfReader(input_path)
    writer = PdfWriter()

    for i, page in enumerate(reader.pages, start=1):
        left, right = split_page_into_left_right(page)
        # Page order is "left → right". Change the order here if needed.
        writer.add_page(left)
        writer.add_page(right)

    # Copy minimal metadata (extend this for full metadata transfer if required)
    if reader.metadata:
        writer.add_metadata(reader.metadata)

    with open(output_path, "wb") as f:
        writer.write(f)

def main():
    if len(sys.argv) != 3:
        print("Usage: python split_pdf_halves.py input.pdf output.pdf")
        sys.exit(1)

    input_pdf = Path(sys.argv[1])
    output_pdf = Path(sys.argv[2])

    if not input_pdf.exists():
        print(f"Input file not found: {input_pdf}")
        sys.exit(1)

    split_pdf(str(input_pdf), str(output_pdf))
    print(f"Done: Created {output_pdf}.")

if __name__ == "__main__":
    main()